[PATCH] gdb: LoongArch: Add internal TLS support

[PATCH] gdb: LoongArch: Add internal TLS support

[Hui Li]

Implements the LoongArch-specific get_tls_dtv_addr() and uses
svr4_tls_register_tls_methods() to register it, together with
svr4_tls_get_thread_local_address as the get_thread_local_address
gdbarch method, to support internal TLS address lookup.

LoongArch doesn't need get_tls_dtp_offset since musl's DTP_OFFSET
is defined as 0.

This is the LoongArch version of commit c34309bea22
("Internal TLS support for aarch64, x86_64, riscv, ppc64, and s390x").

Depends-On: bfc3ac0d13b
("LoongArch: Support R_LARCH_TLS_DTPREL32/64 used in debug section")

Before:

make check-gdb TESTS="gdb.base/tls-nothreads.exp"
=== gdb Summary ===

  # of expected passes		101
  # of known failures		48

make check-gdb TESTS="gdb.base/tls-dlobj.exp"
=== gdb Summary ===

  # of expected passes		261

After:

make check-gdb TESTS="gdb.base/tls-nothreads.exp"
=== gdb Summary ===

  # of expected passes		302

make check-gdb TESTS="gdb.base/tls-dlobj.exp"
=== gdb Summary ===

  # of expected passes		523

Signed-off-by: Hui Li <lihui@loongson.cn>
---
 gdb/arch/loongarch.h                      |  1 +
 gdb/configure.tgt                         |  2 +-
 gdb/loongarch-linux-tdep.c                | 54 +++++++++++++++++++++++
 gdb/testsuite/gdb.base/tls-common.exp.tcl |  2 +-
 4 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/gdb/arch/loongarch.h b/gdb/arch/loongarch.h
index ee9d378afd6..ec3d0d195c9 100644
--- a/gdb/arch/loongarch.h
+++ b/gdb/arch/loongarch.h
@@ -26,6 +26,7 @@
 enum loongarch_regnum
 {
   LOONGARCH_RA_REGNUM = 1,		/* Return Address.  */
+  LOONGARCH_TP_REGNUM = 2,		/* Thread Pointer.  */
   LOONGARCH_SP_REGNUM = 3,		/* Stack Pointer.  */
   LOONGARCH_A0_REGNUM = 4,		/* First Argument/Return Value.  */
   LOONGARCH_A7_REGNUM = 11,		/* Seventh Argument/Syscall Number.  */
diff --git a/gdb/configure.tgt b/gdb/configure.tgt
index 362de60065c..7313b31e42a 100644
--- a/gdb/configure.tgt
+++ b/gdb/configure.tgt
@@ -374,7 +374,7 @@ loongarch*-*-linux*)
 	# Target: LoongArch running Linux
 	gdb_target_obs="loongarch-linux-tdep.o glibc-tdep.o \
 			linux-tdep.o solib-svr4.o solib-svr4-linux.o \
-			linux-record.o"
+			linux-record.o svr4-tls-tdep.o"
 	;;
 
 m32c-*-*)
diff --git a/gdb/loongarch-linux-tdep.c b/gdb/loongarch-linux-tdep.c
index bab84fd126a..9ccb26914a7 100644
--- a/gdb/loongarch-linux-tdep.c
+++ b/gdb/loongarch-linux-tdep.c
@@ -26,6 +26,7 @@
 #include "linux-record.h"
 #include "linux-tdep.h"
 #include "solib-svr4-linux.h"
+#include "svr4-tls-tdep.h"
 #include "loongarch-tdep.h"
 #include "record-full.h"
 #include "regset.h"
@@ -1137,6 +1138,57 @@ init_loongarch_linux_record_tdep (struct gdbarch *gdbarch)
   loongarch_linux_record_tdep.arg7 = LOONGARCH_A0_REGNUM + 6;
 }
 
+/* Fetch and return the TLS DTV (dynamic thread vector) address for PTID.
+   Throw a suitable TLS error if something goes wrong.  */
+
+static CORE_ADDR
+loongarch_linux_get_tls_dtv_addr (struct gdbarch *gdbarch, ptid_t ptid,
+				  svr4_tls_libc libc)
+{
+  /* On LoongArch, the thread pointer is found in TP.  */
+  regcache *regcache
+    = get_thread_arch_regcache (current_inferior (), ptid, gdbarch);
+  target_fetch_registers (regcache, LOONGARCH_TP_REGNUM);
+  ULONGEST thr_ptr;
+  if (regcache->cooked_read (LOONGARCH_TP_REGNUM, &thr_ptr) != REG_VALID)
+    throw_error (TLS_GENERIC_ERROR, _("Unable to fetch thread pointer"));
+
+  CORE_ADDR dtv_ptr_addr;
+  switch (libc)
+    {
+      case svr4_tls_libc_musl:
+	/* MUSL: The DTV pointer is found at the very end of the pthread
+	   struct which is located *before* the thread pointer.  I.e.
+	   the thread pointer will be just beyond the end of the struct,
+	   so the address of the DTV pointer is found one pointer-size
+	   before the thread pointer.  */
+	dtv_ptr_addr = thr_ptr - (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);
+	break;
+      case svr4_tls_libc_glibc:
+	/* GLIBC:  The thread pointer (TP) points just beyond the end of
+	   the TCB (thread control block).  On LoongArch, this struct
+	   (tcbhead_t) is defined to contain two pointers.  The first is
+	   a pointer to the DTV and the second is a pointer to private
+	   data.  So the DTV pointer address is found two pointer-size
+	   before thread pointer.  */
+
+	dtv_ptr_addr = thr_ptr - 2 * (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);
+	break;
+      default:
+	throw_error (TLS_GENERIC_ERROR, _("Unknown LoongArch C library"));
+	break;
+    }
+
+  gdb::byte_vector buf (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);
+  if (target_read_memory (dtv_ptr_addr, buf.data (), buf.size ()) != 0)
+    throw_error (TLS_GENERIC_ERROR, _("Unable to fetch DTV address"));
+
+  const struct builtin_type *builtin = builtin_type (gdbarch);
+  CORE_ADDR dtv_addr = gdbarch_pointer_to_address
+			 (gdbarch, builtin->builtin_data_ptr, buf.data ());
+  return dtv_addr;
+}
+
 /* Initialize LoongArch Linux ABI info.  */
 
 static void
@@ -1158,6 +1210,8 @@ loongarch_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 
   /* Enable TLS support.  */
   set_gdbarch_fetch_tls_load_module_address (gdbarch, svr4_fetch_objfile_link_map);
+  set_gdbarch_get_thread_local_address (gdbarch, svr4_tls_get_thread_local_address);
+  svr4_tls_register_tls_methods (info, gdbarch, loongarch_linux_get_tls_dtv_addr);
 
   /* Prepend tramp frame unwinder for signal.  */
   tramp_frame_prepend_unwinder (gdbarch, &loongarch_linux_rt_sigframe);
diff --git a/gdb/testsuite/gdb.base/tls-common.exp.tcl b/gdb/testsuite/gdb.base/tls-common.exp.tcl
index 06cab649519..53ed1ca4d8a 100644
--- a/gdb/testsuite/gdb.base/tls-common.exp.tcl
+++ b/gdb/testsuite/gdb.base/tls-common.exp.tcl
@@ -26,7 +26,7 @@ require {is_any_target "*-*-linux*"}
 
 set internal_tls_linux_targets {"x86_64-*-linux*" "aarch64-*-linux*"
 				"riscv*-*-linux*" "powerpc64*-*-linux*"
-				"s390x*-*-linux*"}
+				"s390x*-*-linux*" "loongarch*-*-linux*"}
 
 # The "maint set force-internal-tls-address-lookup" command is only
 # available for certain Linux architectures.  Don't attempt to force
-- 
2.48.1

Re: [PATCH] gdb: LoongArch: Add internal TLS support

[Simon Marchi]

On 7/13/26 6:37 AM, Hui Li wrote:
> Implements the LoongArch-specific get_tls_dtv_addr() and uses
> svr4_tls_register_tls_methods() to register it, together with
> svr4_tls_get_thread_local_address as the get_thread_local_address
> gdbarch method, to support internal TLS address lookup.
> 
> LoongArch doesn't need get_tls_dtp_offset since musl's DTP_OFFSET
> is defined as 0.
> 
> This is the LoongArch version of commit c34309bea22
> ("Internal TLS support for aarch64, x86_64, riscv, ppc64, and s390x").
> 
> Depends-On: bfc3ac0d13b
> ("LoongArch: Support R_LARCH_TLS_DTPREL32/64 used in debug section")
> 
> Before:
> 
> make check-gdb TESTS="gdb.base/tls-nothreads.exp"
> === gdb Summary ===
> 
>   # of expected passes		101
>   # of known failures		48
> 
> make check-gdb TESTS="gdb.base/tls-dlobj.exp"
> === gdb Summary ===
> 
>   # of expected passes		261
> 
> After:
> 
> make check-gdb TESTS="gdb.base/tls-nothreads.exp"
> === gdb Summary ===
> 
>   # of expected passes		302
> 
> make check-gdb TESTS="gdb.base/tls-dlobj.exp"
> === gdb Summary ===
> 
>   # of expected passes		523
> 
> Signed-off-by: Hui Li <lihui@loongson.cn>

Great, thanks.  I compared the implementation to Aarch64, and it's very
similar, so it looks reasonable to me.

One nit below:

> @@ -1137,6 +1138,57 @@ init_loongarch_linux_record_tdep (struct gdbarch *gdbarch)
>    loongarch_linux_record_tdep.arg7 = LOONGARCH_A0_REGNUM + 6;
>  }
>  
> +/* Fetch and return the TLS DTV (dynamic thread vector) address for PTID.
> +   Throw a suitable TLS error if something goes wrong.  */
> +
> +static CORE_ADDR
> +loongarch_linux_get_tls_dtv_addr (struct gdbarch *gdbarch, ptid_t ptid,
> +				  svr4_tls_libc libc)
> +{
> +  /* On LoongArch, the thread pointer is found in TP.  */
> +  regcache *regcache
> +    = get_thread_arch_regcache (current_inferior (), ptid, gdbarch);
> +  target_fetch_registers (regcache, LOONGARCH_TP_REGNUM);
> +  ULONGEST thr_ptr;
> +  if (regcache->cooked_read (LOONGARCH_TP_REGNUM, &thr_ptr) != REG_VALID)
> +    throw_error (TLS_GENERIC_ERROR, _("Unable to fetch thread pointer"));
> +
> +  CORE_ADDR dtv_ptr_addr;
> +  switch (libc)
> +    {
> +      case svr4_tls_libc_musl:
> +	/* MUSL: The DTV pointer is found at the very end of the pthread
> +	   struct which is located *before* the thread pointer.  I.e.
> +	   the thread pointer will be just beyond the end of the struct,
> +	   so the address of the DTV pointer is found one pointer-size
> +	   before the thread pointer.  */
> +	dtv_ptr_addr = thr_ptr - (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);
> +	break;
> +      case svr4_tls_libc_glibc:
> +	/* GLIBC:  The thread pointer (TP) points just beyond the end of
> +	   the TCB (thread control block).  On LoongArch, this struct
> +	   (tcbhead_t) is defined to contain two pointers.  The first is
> +	   a pointer to the DTV and the second is a pointer to private
> +	   data.  So the DTV pointer address is found two pointer-size
> +	   before thread pointer.  */
> +
> +	dtv_ptr_addr = thr_ptr - 2 * (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);

Remove empty line above.

With, this:

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon

Re: [PATCH] gdb: LoongArch: Add internal TLS support

[Tiezhu Yang]

On 7/13/26 20:20, Simon Marchi wrote:
> On 7/13/26 6:37 AM, Hui Li wrote:
>> Implements the LoongArch-specific get_tls_dtv_addr() and uses
>> svr4_tls_register_tls_methods() to register it, together with
>> svr4_tls_get_thread_local_address as the get_thread_local_address
>> gdbarch method, to support internal TLS address lookup.

...

>> +	   before thread pointer.  */
>> +
>> +	dtv_ptr_addr = thr_ptr - 2 * (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);
> 
> Remove empty line above.
> 
> With, this:
> 
> Approved-By: Simon Marchi <simon.marchi@efficios.com>

After removing the empty line, pushed.

Thanks,
Tiezhu