[PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[simon.marchi]

From: Simon Marchi <simon.marchi@polymtl.ca>

Tom de Vries reported [1] that a use of the `t` printf length modifier
(used for ptrdiff_t) breaks "set debug dwarf-die 1":

    +break -qualified main
    Reading Reading compcomp unit at offset  unit at offset 0x00x39

    Reading comp unit at offset 0x1a8
    Reading comp unit at offset 0x1e9
    Reading comp unit at offset 0x2c5
    Reading comp unit at offset 0x2a2
    Reading comp unit at offset 0x904
    Unrecognized format specifier 't' in printf

This use is in dwarf2/read.c:

      gdb_printf (gdb_stdlog, "Read die from %s@0x%tx of %s:\n",
		  m_die_section->get_name (),
		  (begin_info_ptr - m_die_section->buffer),
		  bfd_get_filename (m_abfd));

Add support for the `t` length modifier in format_pieces, which
gdb_printf ultimately uses (through ui_out::vmessage).  Modify the three
users of format_pieces: gdb's printf command, gdb's ui_out::vmessage
function and gdbserver's ax_printf function.

The implementation is mostly copied from what we do for size_t.

Since format_pieces is also used to implement the printf command, this
patch brings user-visible changes.  Before:

    (gdb) printf "%td\n", -123
    ❌️ Unrecognized format specifier 't' in printf

After:

    (gdb) printf "%td\n", -123
    -123

[1] https://inbox.sourceware.org/gdb-patches/d4ccce34-aad5-4e3d-8fc9-efb2fc11275c@suse.de/

Change-Id: Ie9fce78f5f48082d8f8a9ca2847b5ae26acaa60d
---
 gdb/printcmd.c                          | 10 ++++++++++
 gdb/testsuite/gdb.base/printcmds.c      |  6 ++++++
 gdb/testsuite/gdb.base/printcmds.exp    |  4 ++++
 gdb/ui-out.c                            | 18 ++++++++++++++++++
 gdb/unittests/format_pieces-selftests.c | 12 ++++++++----
 gdbserver/ax.cc                         |  8 ++++++++
 gdbsupport/format.cc                    | 11 ++++++++++-
 gdbsupport/format.h                     |  2 +-
 8 files changed, 65 insertions(+), 6 deletions(-)

diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 783b83615d02..7c97fc719926 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -2815,6 +2815,16 @@ ui_printf (const char *arg, struct ui_file *stream)
 	    {
 	      size_t val = value_as_long (val_args[i]);
 
+	      DIAGNOSTIC_PUSH
+	      DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
+		gdb_printf (stream, current_substring, val);
+	      DIAGNOSTIC_POP
+	      break;
+	    }
+	  case ptrdiff_t_arg:
+	    {
+	      ptrdiff_t val = value_as_long (val_args[i]);
+
 	      DIAGNOSTIC_PUSH
 	      DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
 		gdb_printf (stream, current_substring, val);
diff --git a/gdb/testsuite/gdb.base/printcmds.c b/gdb/testsuite/gdb.base/printcmds.c
index 8445fcc1aa2a..82796932e1d3 100644
--- a/gdb/testsuite/gdb.base/printcmds.c
+++ b/gdb/testsuite/gdb.base/printcmds.c
@@ -2,6 +2,8 @@
    It is explicitly unsigned to avoid differences due to native characters
    being either signed or unsigned. */
 #include <stdlib.h>
+#include <stddef.h>
+
 unsigned char ctable1[256] = {
   0000, 0001, 0002, 0003, 0004, 0005, 0006, 0007,
   0010, 0011, 0012, 0013, 0014, 0015, 0016, 0017,
@@ -77,6 +79,10 @@ charptr teststring2 = "more contents";
 
 const char *teststring3 = "this is a longer test string that we can use";
 
+/* For testing printf with %z (size_t) and %t (ptrdiff_t) length modifiers.  */
+size_t test_size = 1234;
+ptrdiff_t test_ptrdiff = -5678;
+
 /* Test printing of a struct containing character arrays. */
 
 struct some_arrays {
diff --git a/gdb/testsuite/gdb.base/printcmds.exp b/gdb/testsuite/gdb.base/printcmds.exp
index bc100f93df9a..32a952f01a55 100644
--- a/gdb/testsuite/gdb.base/printcmds.exp
+++ b/gdb/testsuite/gdb.base/printcmds.exp
@@ -908,6 +908,10 @@ proc test_printf {} {
     # PR cli/14977.
     gdb_test "printf \"%s\\n\", 0" "\\(null\\)"
 
+    # Test %z (size_t) and %t (ptrdiff_t) length modifiers.
+    gdb_test "printf \"%zu\\n\", test_size" "1234"
+    gdb_test "printf \"%td\\n\", test_ptrdiff" "-5678"
+
     with_max_value_size 20 {
 	gdb_test {printf "%s", teststring3} \
 	    "^printed string requires 45 bytes, which is more than max-value-size"
diff --git a/gdb/ui-out.c b/gdb/ui-out.c
index 4f20e6b93477..87874e22530f 100644
--- a/gdb/ui-out.c
+++ b/gdb/ui-out.c
@@ -682,6 +682,24 @@ ui_out::vmessage (const ui_file_style &in_style, const char *format,
 	      }
 	  }
 	  break;
+	case ptrdiff_t_arg:
+	  {
+	    ptrdiff_t val = va_arg (args, ptrdiff_t);
+	    switch (piece.n_int_args)
+	      {
+	      case 0:
+		call_do_message (style, current_substring, val);
+		break;
+	      case 1:
+		call_do_message (style, current_substring, intvals[0], val);
+		break;
+	      case 2:
+		call_do_message (style, current_substring,
+				 intvals[0], intvals[1], val);
+		break;
+	      }
+	  }
+	  break;
 	case double_arg:
 	  call_do_message (style, current_substring, va_arg (args, double));
 	  break;
diff --git a/gdb/unittests/format_pieces-selftests.c b/gdb/unittests/format_pieces-selftests.c
index af574ccc900f..c5f3cf74f1dc 100644
--- a/gdb/unittests/format_pieces-selftests.c
+++ b/gdb/unittests/format_pieces-selftests.c
@@ -105,40 +105,44 @@ test_gdb_formats ()
 static void
 test_format_int_sizes ()
 {
-  check ("Hello\\t %hu%lu%llu%zu", /* ARI: %ll */
+  check ("Hello\\t %hu%lu%llu%zu%tu", /* ARI: %ll */
     {
       {"Hello\t ", literal_piece, 0},
       {"%hu", int_arg, 0},
       {"%lu", long_arg, 0},
       {"%" LL "u", long_long_arg, 0},
       {"%zu", size_t_arg, 0},
+      {"%tu", ptrdiff_t_arg, 0},
     });
 
-  check ("Hello\\t %hx%lx%llx%zx", /* ARI: %ll */
+  check ("Hello\\t %hx%lx%llx%zx%tx", /* ARI: %ll */
     {
       {"Hello\t ", literal_piece, 0},
       {"%hx", int_arg, 0},
       {"%lx", long_arg, 0},
       {"%" LL "x", long_long_arg, 0},
       {"%zx", size_t_arg, 0},
+      {"%tx", ptrdiff_t_arg, 0},
     });
 
-  check ("Hello\\t %ho%lo%llo%zo", /* ARI: %ll */
+  check ("Hello\\t %ho%lo%llo%zo%to", /* ARI: %ll */
     {
       {"Hello\t ", literal_piece, 0},
       {"%ho", int_arg, 0},
       {"%lo", long_arg, 0},
       {"%" LL "o", long_long_arg, 0},
       {"%zo", size_t_arg, 0},
+      {"%to", ptrdiff_t_arg, 0},
     });
 
-  check ("Hello\\t %hd%ld%lld%zd", /* ARI: %ll */
+  check ("Hello\\t %hd%ld%lld%zd%td", /* ARI: %ll */
     {
       {"Hello\t ", literal_piece, 0},
       {"%hd", int_arg, 0},
       {"%ld", long_arg, 0},
       {"%" LL "d", long_long_arg, 0},
       {"%zd", size_t_arg, 0},
+      {"%td", ptrdiff_t_arg, 0},
     });
 }
 
diff --git a/gdbserver/ax.cc b/gdbserver/ax.cc
index 44fcf3157291..4993bed2532c 100644
--- a/gdbserver/ax.cc
+++ b/gdbserver/ax.cc
@@ -908,6 +908,14 @@ ax_printf (CORE_ADDR fn, CORE_ADDR chan, const char *format,
 	    break;
 	  }
 
+	case ptrdiff_t_arg:
+	  {
+	    ptrdiff_t val = args[i];
+
+	    printf (current_substring, val);
+	    break;
+	  }
+
 	case literal_piece:
 	  /* Print a portion of the format string that has no
 	     directives.  Note that this will not include any
diff --git a/gdbsupport/format.cc b/gdbsupport/format.cc
index b515a95114e0..43995edf453e 100644
--- a/gdbsupport/format.cc
+++ b/gdbsupport/format.cc
@@ -111,6 +111,7 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
 	int seen_big_l = 0, seen_h = 0, seen_big_h = 0;
 	int seen_big_d = 0, seen_double_big_d = 0;
 	int seen_size_t = 0;
+	int seen_ptrdiff_t = 0;
 	int bad = 0;
 	int n_int_args = 0;
 	bool seen_i64 = false;
@@ -224,6 +225,11 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
 	    seen_size_t = 1;
 	    f++;
 	    break;
+	  case 't':
+	    /* For ptrdiff_t.  */
+	    seen_ptrdiff_t = 1;
+	    f++;
+	    break;
 	  case 'I':
 	    /* Support the Windows '%I64' extension, because an
 	       earlier call to format_pieces might have converted %lld
@@ -257,6 +263,8 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
 	  case 'i':
 	    if (seen_size_t)
 	      this_argclass = size_t_arg;
+	    else if (seen_ptrdiff_t)
+	      this_argclass = ptrdiff_t_arg;
 	    else if (lcount == 0)
 	      this_argclass = int_arg;
 	    else if (lcount == 1)
@@ -334,7 +342,8 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
 
 	    if (lcount > 1 || seen_h || seen_big_h || seen_big_h
 		|| seen_big_d || seen_double_big_d || seen_size_t
-		|| seen_prec || seen_zero || seen_space || seen_plus)
+		|| seen_ptrdiff_t || seen_prec || seen_zero || seen_space
+		|| seen_plus)
 	      bad = 1;
 
 	    this_argclass = value_arg;
diff --git a/gdbsupport/format.h b/gdbsupport/format.h
index 91bcf1db55a6..ced10e46a716 100644
--- a/gdbsupport/format.h
+++ b/gdbsupport/format.h
@@ -36,7 +36,7 @@
 enum argclass
   {
     literal_piece,
-    int_arg, long_arg, long_long_arg, size_t_arg, ptr_arg,
+    int_arg, long_arg, long_long_arg, size_t_arg, ptrdiff_t_arg, ptr_arg,
     string_arg, wide_string_arg, wide_char_arg,
     double_arg, long_double_arg,
     dec32float_arg, dec64float_arg, dec128float_arg,

base-commit: b9517052ce5c1d87bfd7030bcbf90a98f63fddf6
-- 
2.52.0

Re: [PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[Tom Tromey]

>>>>> "Simon" == simon marchi <simon.marchi@polymtl.ca> writes:

Simon> Add support for the `t` length modifier in format_pieces, which
Simon> gdb_printf ultimately uses (through ui_out::vmessage).  Modify the three
Simon> users of format_pieces: gdb's printf command, gdb's ui_out::vmessage
Simon> function and gdbserver's ax_printf function.

Thanks.

These modifiers are one of the clearest reasons that printf should be
replaced.  I think we should generally avoid them.  We've already got
plongest, etc; which seem safer.  See commit a1537331 (the "other
direction") but there's also commit a5adb8f3 and probably more.

Anyway, it's ok.
Approved-By: Tom Tromey <tom@tromey.com>

Tom

Re: [PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[Simon Marchi]

On 1/15/26 2:24 PM, Tom Tromey wrote:
>>>>>> "Simon" == simon marchi <simon.marchi@polymtl.ca> writes:
> 
> Simon> Add support for the `t` length modifier in format_pieces, which
> Simon> gdb_printf ultimately uses (through ui_out::vmessage).  Modify the three
> Simon> users of format_pieces: gdb's printf command, gdb's ui_out::vmessage
> Simon> function and gdbserver's ax_printf function.
> 
> Thanks.
> 
> These modifiers are one of the clearest reasons that printf should be
> replaced.  I think we should generally avoid them.  We've already got
> plongest, etc; which seem safer.  See commit a1537331 (the "other
> direction") but there's also commit a5adb8f3 and probably more.
> 
> Anyway, it's ok.
> Approved-By: Tom Tromey <tom@tromey.com>
> 
> Tom

I think the reason for plongest is more that LONGEST can vary from build
to build.  We could otherwise have PRILONGEST / PRIULONGEST / etc
macros, just like there is PRIu64 & co.  But yeah if we do a move
nowadays, it would make more sense to move to std::format/{fmt}.

I pushed the patch, thanks.

Simon

Re: [PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[Tom Tromey]

>>>>> "Simon" == Simon Marchi <simon.marchi@polymtl.ca> writes:

Simon> I think the reason for plongest is more that LONGEST can vary from build
Simon> to build.  We could otherwise have PRILONGEST / PRIULONGEST / etc
Simon> macros, just like there is PRIu64 & co.

We could have those but personally I think those PRI* things are
unreadably ugly.

As an aside, it's absurd for the gdb "printf" command to use these at
all.  gdb already knows all the types, "%d" could easily handle any
integral type and "%td" is never truly necessary.

Tom

Re: [PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[Guinevere Larsen]

On 1/12/26 3:24 PM, simon.marchi@polymtl.ca wrote:
> From: Simon Marchi <simon.marchi@polymtl.ca>
>
> Tom de Vries reported [1] that a use of the `t` printf length modifier
> (used for ptrdiff_t) breaks "set debug dwarf-die 1":
>
>      +break -qualified main
>      Reading Reading compcomp unit at offset  unit at offset 0x00x39
>
>      Reading comp unit at offset 0x1a8
>      Reading comp unit at offset 0x1e9
>      Reading comp unit at offset 0x2c5
>      Reading comp unit at offset 0x2a2
>      Reading comp unit at offset 0x904
>      Unrecognized format specifier 't' in printf
>
> This use is in dwarf2/read.c:
>
>        gdb_printf (gdb_stdlog, "Read die from %s@0x%tx of %s:\n",
> 		  m_die_section->get_name (),
> 		  (begin_info_ptr - m_die_section->buffer),
> 		  bfd_get_filename (m_abfd));
>
> Add support for the `t` length modifier in format_pieces, which
> gdb_printf ultimately uses (through ui_out::vmessage).  Modify the three
> users of format_pieces: gdb's printf command, gdb's ui_out::vmessage
> function and gdbserver's ax_printf function.
>
> The implementation is mostly copied from what we do for size_t.
>
> Since format_pieces is also used to implement the printf command, this
> patch brings user-visible changes.  Before:
>
>      (gdb) printf "%td\n", -123
>      ❌️ Unrecognized format specifier 't' in printf
>
> After:
>
>      (gdb) printf "%td\n", -123
>      -123
>
> [1] https://inbox.sourceware.org/gdb-patches/d4ccce34-aad5-4e3d-8fc9-efb2fc11275c@suse.de/
>
> Change-Id: Ie9fce78f5f48082d8f8a9ca2847b5ae26acaa60d
> ---

This commit seems to have caused a regression. After this, when starting 
GDB without the quiet flag I get the following:

0x7ffc6b9bc520s
Copyright (C) 2026 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <0x7ffc6b9bc560s>
This is free software: you are free to change and redistribute it
There is NO WARRANTY, to the extent permitted by law.
Type "0x7ffc6b9bc5e0s" and "0x7ffc6b9bc5a0s" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "0x7ffc6b9bc620s" for configuration details.
For bug reporting instructions, please see:
0x7ffc6b9bc660s.

That is, anywhere where GDB would print a styled string, we seem to be 
printing a pointer address instead.

>   gdb/printcmd.c                          | 10 ++++++++++
>   gdb/testsuite/gdb.base/printcmds.c      |  6 ++++++
>   gdb/testsuite/gdb.base/printcmds.exp    |  4 ++++
>   gdb/ui-out.c                            | 18 ++++++++++++++++++
>   gdb/unittests/format_pieces-selftests.c | 12 ++++++++----
>   gdbserver/ax.cc                         |  8 ++++++++
>   gdbsupport/format.cc                    | 11 ++++++++++-
>   gdbsupport/format.h                     |  2 +-
>   8 files changed, 65 insertions(+), 6 deletions(-)
>
> diff --git a/gdb/printcmd.c b/gdb/printcmd.c
> index 783b83615d02..7c97fc719926 100644
> --- a/gdb/printcmd.c
> +++ b/gdb/printcmd.c
> @@ -2815,6 +2815,16 @@ ui_printf (const char *arg, struct ui_file *stream)
>   	    {
>   	      size_t val = value_as_long (val_args[i]);
>   
> +	      DIAGNOSTIC_PUSH
> +	      DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
> +		gdb_printf (stream, current_substring, val);
> +	      DIAGNOSTIC_POP
> +	      break;
> +	    }
> +	  case ptrdiff_t_arg:
> +	    {
> +	      ptrdiff_t val = value_as_long (val_args[i]);
> +
>   	      DIAGNOSTIC_PUSH
>   	      DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
>   		gdb_printf (stream, current_substring, val);
> diff --git a/gdb/testsuite/gdb.base/printcmds.c b/gdb/testsuite/gdb.base/printcmds.c
> index 8445fcc1aa2a..82796932e1d3 100644
> --- a/gdb/testsuite/gdb.base/printcmds.c
> +++ b/gdb/testsuite/gdb.base/printcmds.c
> @@ -2,6 +2,8 @@
>      It is explicitly unsigned to avoid differences due to native characters
>      being either signed or unsigned. */
>   #include <stdlib.h>
> +#include <stddef.h>
> +
>   unsigned char ctable1[256] = {
>     0000, 0001, 0002, 0003, 0004, 0005, 0006, 0007,
>     0010, 0011, 0012, 0013, 0014, 0015, 0016, 0017,
> @@ -77,6 +79,10 @@ charptr teststring2 = "more contents";
>   
>   const char *teststring3 = "this is a longer test string that we can use";
>   
> +/* For testing printf with %z (size_t) and %t (ptrdiff_t) length modifiers.  */
> +size_t test_size = 1234;
> +ptrdiff_t test_ptrdiff = -5678;
> +
>   /* Test printing of a struct containing character arrays. */
>   
>   struct some_arrays {
> diff --git a/gdb/testsuite/gdb.base/printcmds.exp b/gdb/testsuite/gdb.base/printcmds.exp
> index bc100f93df9a..32a952f01a55 100644
> --- a/gdb/testsuite/gdb.base/printcmds.exp
> +++ b/gdb/testsuite/gdb.base/printcmds.exp
> @@ -908,6 +908,10 @@ proc test_printf {} {
>       # PR cli/14977.
>       gdb_test "printf \"%s\\n\", 0" "\\(null\\)"
>   
> +    # Test %z (size_t) and %t (ptrdiff_t) length modifiers.
> +    gdb_test "printf \"%zu\\n\", test_size" "1234"
> +    gdb_test "printf \"%td\\n\", test_ptrdiff" "-5678"
> +
>       with_max_value_size 20 {
>   	gdb_test {printf "%s", teststring3} \
>   	    "^printed string requires 45 bytes, which is more than max-value-size"
> diff --git a/gdb/ui-out.c b/gdb/ui-out.c
> index 4f20e6b93477..87874e22530f 100644
> --- a/gdb/ui-out.c
> +++ b/gdb/ui-out.c
> @@ -682,6 +682,24 @@ ui_out::vmessage (const ui_file_style &in_style, const char *format,
>   	      }
>   	  }
>   	  break;
> +	case ptrdiff_t_arg:
> +	  {
> +	    ptrdiff_t val = va_arg (args, ptrdiff_t);
> +	    switch (piece.n_int_args)
> +	      {
> +	      case 0:
> +		call_do_message (style, current_substring, val);
> +		break;
> +	      case 1:
> +		call_do_message (style, current_substring, intvals[0], val);
> +		break;
> +	      case 2:
> +		call_do_message (style, current_substring,
> +				 intvals[0], intvals[1], val);
> +		break;
> +	      }
> +	  }
> +	  break;
>   	case double_arg:
>   	  call_do_message (style, current_substring, va_arg (args, double));
>   	  break;
> diff --git a/gdb/unittests/format_pieces-selftests.c b/gdb/unittests/format_pieces-selftests.c
> index af574ccc900f..c5f3cf74f1dc 100644
> --- a/gdb/unittests/format_pieces-selftests.c
> +++ b/gdb/unittests/format_pieces-selftests.c
> @@ -105,40 +105,44 @@ test_gdb_formats ()
>   static void
>   test_format_int_sizes ()
>   {
> -  check ("Hello\\t %hu%lu%llu%zu", /* ARI: %ll */
> +  check ("Hello\\t %hu%lu%llu%zu%tu", /* ARI: %ll */
>       {
>         {"Hello\t ", literal_piece, 0},
>         {"%hu", int_arg, 0},
>         {"%lu", long_arg, 0},
>         {"%" LL "u", long_long_arg, 0},
>         {"%zu", size_t_arg, 0},
> +      {"%tu", ptrdiff_t_arg, 0},
>       });
>   
> -  check ("Hello\\t %hx%lx%llx%zx", /* ARI: %ll */
> +  check ("Hello\\t %hx%lx%llx%zx%tx", /* ARI: %ll */
>       {
>         {"Hello\t ", literal_piece, 0},
>         {"%hx", int_arg, 0},
>         {"%lx", long_arg, 0},
>         {"%" LL "x", long_long_arg, 0},
>         {"%zx", size_t_arg, 0},
> +      {"%tx", ptrdiff_t_arg, 0},
>       });
>   
> -  check ("Hello\\t %ho%lo%llo%zo", /* ARI: %ll */
> +  check ("Hello\\t %ho%lo%llo%zo%to", /* ARI: %ll */
>       {
>         {"Hello\t ", literal_piece, 0},
>         {"%ho", int_arg, 0},
>         {"%lo", long_arg, 0},
>         {"%" LL "o", long_long_arg, 0},
>         {"%zo", size_t_arg, 0},
> +      {"%to", ptrdiff_t_arg, 0},
>       });
>   
> -  check ("Hello\\t %hd%ld%lld%zd", /* ARI: %ll */
> +  check ("Hello\\t %hd%ld%lld%zd%td", /* ARI: %ll */
>       {
>         {"Hello\t ", literal_piece, 0},
>         {"%hd", int_arg, 0},
>         {"%ld", long_arg, 0},
>         {"%" LL "d", long_long_arg, 0},
>         {"%zd", size_t_arg, 0},
> +      {"%td", ptrdiff_t_arg, 0},
>       });
>   }
>   
> diff --git a/gdbserver/ax.cc b/gdbserver/ax.cc
> index 44fcf3157291..4993bed2532c 100644
> --- a/gdbserver/ax.cc
> +++ b/gdbserver/ax.cc
> @@ -908,6 +908,14 @@ ax_printf (CORE_ADDR fn, CORE_ADDR chan, const char *format,
>   	    break;
>   	  }
>   
> +	case ptrdiff_t_arg:
> +	  {
> +	    ptrdiff_t val = args[i];
> +
> +	    printf (current_substring, val);
> +	    break;
> +	  }
> +
>   	case literal_piece:
>   	  /* Print a portion of the format string that has no
>   	     directives.  Note that this will not include any
> diff --git a/gdbsupport/format.cc b/gdbsupport/format.cc
> index b515a95114e0..43995edf453e 100644
> --- a/gdbsupport/format.cc
> +++ b/gdbsupport/format.cc
> @@ -111,6 +111,7 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
>   	int seen_big_l = 0, seen_h = 0, seen_big_h = 0;
>   	int seen_big_d = 0, seen_double_big_d = 0;
>   	int seen_size_t = 0;
> +	int seen_ptrdiff_t = 0;
>   	int bad = 0;
>   	int n_int_args = 0;
>   	bool seen_i64 = false;
> @@ -224,6 +225,11 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
>   	    seen_size_t = 1;
>   	    f++;
>   	    break;
> +	  case 't':
> +	    /* For ptrdiff_t.  */
> +	    seen_ptrdiff_t = 1;
> +	    f++;
> +	    break;
>   	  case 'I':
>   	    /* Support the Windows '%I64' extension, because an
>   	       earlier call to format_pieces might have converted %lld
> @@ -257,6 +263,8 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
>   	  case 'i':
>   	    if (seen_size_t)
>   	      this_argclass = size_t_arg;
> +	    else if (seen_ptrdiff_t)
> +	      this_argclass = ptrdiff_t_arg;
>   	    else if (lcount == 0)
>   	      this_argclass = int_arg;
>   	    else if (lcount == 1)
> @@ -334,7 +342,8 @@ format_pieces::format_pieces (const char **arg, bool gdb_extensions,
>   
>   	    if (lcount > 1 || seen_h || seen_big_h || seen_big_h
>   		|| seen_big_d || seen_double_big_d || seen_size_t
> -		|| seen_prec || seen_zero || seen_space || seen_plus)
> +		|| seen_ptrdiff_t || seen_prec || seen_zero || seen_space
> +		|| seen_plus)
>   	      bad = 1;
>   
>   	    this_argclass = value_arg;
> diff --git a/gdbsupport/format.h b/gdbsupport/format.h
> index 91bcf1db55a6..ced10e46a716 100644
> --- a/gdbsupport/format.h
> +++ b/gdbsupport/format.h
> @@ -36,7 +36,7 @@
>   enum argclass
>     {
>       literal_piece,
> -    int_arg, long_arg, long_long_arg, size_t_arg, ptr_arg,
> +    int_arg, long_arg, long_long_arg, size_t_arg, ptrdiff_t_arg, ptr_arg,
>       string_arg, wide_string_arg, wide_char_arg,
>       double_arg, long_double_arg,
>       dec32float_arg, dec64float_arg, dec128float_arg,
>
> base-commit: b9517052ce5c1d87bfd7030bcbf90a98f63fddf6


-- 
Cheers,
Guinevere Larsen
It/she

Re: [PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[Simon Marchi]

On 1/19/26 12:29 PM, Guinevere Larsen wrote:
> On 1/12/26 3:24 PM, simon.marchi@polymtl.ca wrote:
>> From: Simon Marchi <simon.marchi@polymtl.ca>
>>
>> Tom de Vries reported [1] that a use of the `t` printf length modifier
>> (used for ptrdiff_t) breaks "set debug dwarf-die 1":
>>
>>      +break -qualified main
>>      Reading Reading compcomp unit at offset  unit at offset 0x00x39
>>
>>      Reading comp unit at offset 0x1a8
>>      Reading comp unit at offset 0x1e9
>>      Reading comp unit at offset 0x2c5
>>      Reading comp unit at offset 0x2a2
>>      Reading comp unit at offset 0x904
>>      Unrecognized format specifier 't' in printf
>>
>> This use is in dwarf2/read.c:
>>
>>        gdb_printf (gdb_stdlog, "Read die from %s@0x%tx of %s:\n",
>>           m_die_section->get_name (),
>>           (begin_info_ptr - m_die_section->buffer),
>>           bfd_get_filename (m_abfd));
>>
>> Add support for the `t` length modifier in format_pieces, which
>> gdb_printf ultimately uses (through ui_out::vmessage).  Modify the three
>> users of format_pieces: gdb's printf command, gdb's ui_out::vmessage
>> function and gdbserver's ax_printf function.
>>
>> The implementation is mostly copied from what we do for size_t.
>>
>> Since format_pieces is also used to implement the printf command, this
>> patch brings user-visible changes.  Before:
>>
>>      (gdb) printf "%td\n", -123
>>      ❌️ Unrecognized format specifier 't' in printf
>>
>> After:
>>
>>      (gdb) printf "%td\n", -123
>>      -123
>>
>> [1] https://inbox.sourceware.org/gdb-patches/d4ccce34-aad5-4e3d-8fc9-efb2fc11275c@suse.de/
>>
>> Change-Id: Ie9fce78f5f48082d8f8a9ca2847b5ae26acaa60d
>> ---
> 
> This commit seems to have caused a regression. After this, when starting GDB without the quiet flag I get the following:
> 
> 0x7ffc6b9bc520s
> Copyright (C) 2026 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <0x7ffc6b9bc560s>
> This is free software: you are free to change and redistribute it
> There is NO WARRANTY, to the extent permitted by law.
> Type "0x7ffc6b9bc5e0s" and "0x7ffc6b9bc5a0s" for details.
> This GDB was configured as "x86_64-pc-linux-gnu".
> Type "0x7ffc6b9bc620s" for configuration details.
> For bug reporting instructions, please see:
> 0x7ffc6b9bc660s.
> 
> That is, anywhere where GDB would print a styled string, we seem to be printing a pointer address instead.


Hmm, I don't see this.  I see a pink "GNU gdb (GDB)
18.0.50.20260119-git" where you see the "0x7ffc6b9bc660s".
We will need to figure out what is different between our setups.

Simon

Re: [PATCH] gdb, gdbsupport, gdbserver: add support for printf 't' length modifier

[Guinevere Larsen]

On 1/19/26 3:09 PM, Simon Marchi wrote:
> On 1/19/26 12:29 PM, Guinevere Larsen wrote:
>> On 1/12/26 3:24 PM, simon.marchi@polymtl.ca wrote:
>>> From: Simon Marchi <simon.marchi@polymtl.ca>
>>>
>>> Tom de Vries reported [1] that a use of the `t` printf length modifier
>>> (used for ptrdiff_t) breaks "set debug dwarf-die 1":
>>>
>>>       +break -qualified main
>>>       Reading Reading compcomp unit at offset  unit at offset 0x00x39
>>>
>>>       Reading comp unit at offset 0x1a8
>>>       Reading comp unit at offset 0x1e9
>>>       Reading comp unit at offset 0x2c5
>>>       Reading comp unit at offset 0x2a2
>>>       Reading comp unit at offset 0x904
>>>       Unrecognized format specifier 't' in printf
>>>
>>> This use is in dwarf2/read.c:
>>>
>>>         gdb_printf (gdb_stdlog, "Read die from %s@0x%tx of %s:\n",
>>>            m_die_section->get_name (),
>>>            (begin_info_ptr - m_die_section->buffer),
>>>            bfd_get_filename (m_abfd));
>>>
>>> Add support for the `t` length modifier in format_pieces, which
>>> gdb_printf ultimately uses (through ui_out::vmessage).  Modify the three
>>> users of format_pieces: gdb's printf command, gdb's ui_out::vmessage
>>> function and gdbserver's ax_printf function.
>>>
>>> The implementation is mostly copied from what we do for size_t.
>>>
>>> Since format_pieces is also used to implement the printf command, this
>>> patch brings user-visible changes.  Before:
>>>
>>>       (gdb) printf "%td\n", -123
>>>       ❌️ Unrecognized format specifier 't' in printf
>>>
>>> After:
>>>
>>>       (gdb) printf "%td\n", -123
>>>       -123
>>>
>>> [1] https://inbox.sourceware.org/gdb-patches/d4ccce34-aad5-4e3d-8fc9-efb2fc11275c@suse.de/
>>>
>>> Change-Id: Ie9fce78f5f48082d8f8a9ca2847b5ae26acaa60d
>>> ---
>> This commit seems to have caused a regression. After this, when starting GDB without the quiet flag I get the following:
>>
>> 0x7ffc6b9bc520s
>> Copyright (C) 2026 Free Software Foundation, Inc.
>> License GPLv3+: GNU GPL version 3 or later <0x7ffc6b9bc560s>
>> This is free software: you are free to change and redistribute it
>> There is NO WARRANTY, to the extent permitted by law.
>> Type "0x7ffc6b9bc5e0s" and "0x7ffc6b9bc5a0s" for details.
>> This GDB was configured as "x86_64-pc-linux-gnu".
>> Type "0x7ffc6b9bc620s" for configuration details.
>> For bug reporting instructions, please see:
>> 0x7ffc6b9bc660s.
>>
>> That is, anywhere where GDB would print a styled string, we seem to be printing a pointer address instead.
>
> Hmm, I don't see this.  I see a pink "GNU gdb (GDB)
> 18.0.50.20260119-git" where you see the "0x7ffc6b9bc660s".
> We will need to figure out what is different between our setups.
>
> Simon
>
Oh, oops, turns out it was my bad.

I was running make on the gdb subdirectory instead of the build 
directory and never compiled gdbsupport

Once I did that things magically started working again!


Sorry about the noise

-- 
Cheers,
Guinevere Larsen
It/she