[PATCH] gdbserver: Update require_int function to parse offset for pread packet

[Kirill Radkin <kirill.radkin@syntacore.com>]

I've addressed all review comments.
Also, additional information about issue was added to commit message.

---

Recently I have encountered an issue with gdbserver not being able to send debug information from large \
files (> 2Gb). I found that this issue is connected with parsing offsets (integer) from vFile::pread \
packets. There is already a patch (https://sourceware.org/bugzilla/show_bug.cgi?id=23198) that allows to \
parse integers up to 0x7fffffff (32-bit integer), but it doesn't fix the problem at all, because offsets \
can have a off_t type which can be larger than 32-bit integer (it depends on system).

This patch allows require_int() function to parse offset up to the maximum value implied by the off_t \
type.

Currently gdbserver uses require_int() function to parse the requested offset
(in vFile::pread packet and the like). This function allows integers up to
0x7fffffff (to fit in 32-bit int), however the offset (for pread system call)
has an off_t type which can be larger than 32-bit.

This patch allows require_int() function to parse offset up to the maximum
value implied by the off_t type.
---
 gdb/testsuite/gdb.server/pread-offset-size.S  | 29 +++++++++++
 .../gdb.server/pread-offset-size.exp          | 50 +++++++++++++++++++
 gdbserver/hostio.cc                           | 17 +++++--
 3 files changed, 92 insertions(+), 4 deletions(-)
 create mode 100644 gdb/testsuite/gdb.server/pread-offset-size.S
 create mode 100644 gdb/testsuite/gdb.server/pread-offset-size.exp

diff --git a/gdb/testsuite/gdb.server/pread-offset-size.S b/gdb/testsuite/gdb.server/pread-offset-size.S
new file mode 100644
index 00000000000..63b2faa213d
--- /dev/null
+++ b/gdb/testsuite/gdb.server/pread-offset-size.S
@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2025 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Here we are trying to create a large binary (> 2 GB),
+   3742415472 bytes is about 3,5 gigabytes.  */
+
+	.text
+	.globl	_start
+_start:
+	.skip 3742415472
+   ret
+	.globl	f
+	.type	f, @function
+f:
+   ret
diff --git a/gdb/testsuite/gdb.server/pread-offset-size.exp b/gdb/testsuite/gdb.server/pread-offset-size.exp
new file mode 100644
index 00000000000..e224e971ad5
--- /dev/null
+++ b/gdb/testsuite/gdb.server/pread-offset-size.exp
@@ -0,0 +1,50 @@
+# Copyright (C) 2025 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# Testing fix of a problem with gdbserver not being able to send
+# debug information from large files (> 2GB)
+
+load_lib gdbserver-support.exp
+
+require allow_gdbserver_tests
+
+standard_testfile .S
+
+if { [prepare_for_testing ${testfile}.exp $testfile \
+	$srcfile {debug additional_flags=-nostdlib} ] } {
+    return -1
+}
+
+clean_restart
+
+gdb_test_no_output "set remote exec-file $binfile" \
+    "set remote exec-file"
+
+# Make sure we're disconnected, in case we're testing with an
+# extended-remote board, therefore already connected.
+gdb_test "disconnect" ".*"
+
+set res [gdbserver_spawn ""]
+set gdbserver_protocol [lindex $res 0]
+set gdbserver_gdbport [lindex $res 1]
+
+gdb_test "target $gdbserver_protocol $gdbserver_gdbport" \
+    "Remote debugging using .*" \
+    "target $gdbserver_protocol"
+
+# If load of a large binary was successful,
+# we should be able to place a break on f
+
+gdb_test "break f" "Breakpoint 1.*"
diff --git a/gdbserver/hostio.cc b/gdbserver/hostio.cc
index 17b6179d8ca..4e77253750a 100644
--- a/gdbserver/hostio.cc
+++ b/gdbserver/hostio.cc
@@ -89,12 +89,18 @@ require_filename (char **pp, char *filename)
   return 0;
 }
 
+template <typename T>
 static int
-require_int (char **pp, int *value)
+require_int (char **pp, T *value)
 {
+  constexpr bool is_signed = std::is_signed<T>::value;
+
   char *p;
   int count, firstdigit;
 
+  /* Max count of hexadecimal digits in T (1 hex digit is 4 bits).  */
+  int max_count = sizeof (T) * CHAR_BIT / 4;
+
   p = *pp;
   *value = 0;
   count = 0;
@@ -111,7 +117,8 @@ require_int (char **pp, int *value)
 	firstdigit = nib;
 
       /* Don't allow overflow.  */
-      if (count >= 8 || (count == 7 && firstdigit >= 0x8))
+      if (count >= max_count
+	  || (is_signed && count == (max_count - 1) && firstdigit >= 0x8))
 	return -1;
 
       *value = *value * 16 + nib;
@@ -343,7 +350,8 @@ handle_open (char *own_buf)
 static void
 handle_pread (char *own_buf, int *new_packet_len)
 {
-  int fd, ret, len, offset, bytes_sent;
+  int fd, ret, len, bytes_sent;
+  off_t offset;
   char *p, *data;
   static int max_reply_size = -1;
 
@@ -410,7 +418,8 @@ handle_pread (char *own_buf, int *new_packet_len)
 static void
 handle_pwrite (char *own_buf, int packet_len)
 {
-  int fd, ret, len, offset;
+  int fd, ret, len;
+  off_t offset;
   char *p, *data;
 
   p = own_buf + strlen ("vFile:pwrite:");
-- 
2.43.0