From 244a9a81010130aa250171db55fb137b2fd581d9 Mon Sep 17 00:00:00 2001
From: Nils-Christian Kempke <nils-christian.kempke@intel.com>
Date: Thu, 4 Aug 2022 08:52:28 +0200
Subject: [PATCH] gdb, testsuite: adapt function_range expected name

When writing a dwarf testcase for some C++ code I wanted to use the
MACRO_AT_range which in turn uses the function_range proc in dwarf.exp
to extract the bounds of 'main'.

However, the macro failed as GDB prints the C++ 'main' with its
arguments as 'main(int, char**)' or 'main()'.

The reason for this is that in read.c::dwarf2_compute_name we call
c_type_print_args on C++ functions and append their arguments to the
function name.  This happens to all C++ functions, but is only visible
when the function doesn't have a linkage name.

An example might make this more clear.  Given the following code

  >> cat c.cpp
  int foo (int a, float b)
  {
    return 0;
  }

  int main (int argc, char **argv)
  {
    return 0;
  }

which is legal in both languages, C and C++, and compiling it with
e.g. clang or gcc will make the disassemble command look like:

  >> clang --version
  clang version 10.0.0-4ubuntu1
  ...
  >> clang -O0 -g ./c.cpp
  >> gdb -q ./a.out -ex "start"
  ...
  (gdb) disassemble main
  Dump of assembler code for function main(int, char**):
     0x0000000000401120 <+0>:     push   %rbp
     0x0000000000401121 <+1>:     mov    %rsp,%rbp
  ...
     0x0000000000401135 <+21>:    ret
  End of assembler dump.
  (gdb) disassemble foo
  Dump of assembler code for function _Z3fooif:
     0x0000000000401110 <+0>:     push   %rbp
     0x0000000000401111 <+1>:     mov    %rsp,%rbp
  ...
     0x000000000040111f <+15>:    ret
  End of assembler dump.

Note, that main is emitted with its arguments while for foo the linkage
name is being printed, as also visible in its DWARF:

  >> objdump ./a.out --dwarf=info | grep "foo" -A3 -B3
      <2b>   DW_AT_low_pc      : 0x401110
      <33>   DW_AT_high_pc     : 0x10
      <37>   DW_AT_frame_base  : 1 byte block: 56         (DW_OP_reg6 (rbp))
      <39>   DW_AT_linkage_name: (indirect string, offset: 0x39): _Z3fooif
      <3d>   DW_AT_name        : (indirect string, offset: 0x42): foo
      <41>   DW_AT_decl_file   : 1
      <42>   DW_AT_decl_line   : 1
      <43>   DW_AT_type        : <0x9a>

Now, let's rename the C++ file and compile it as C:

  >> mv c.cpp c.c
  >> clang -O0 -g ./c.c
  >> gdb -q ./a.out -ex "start'
  ...
  (gdb) disassemble main
  Dump of assembler code for function main:
     0x0000000000401120 <+0>:     push   %rbp
     0x0000000000401121 <+1>:     mov    %rsp,%rbp
  ...
     0x0000000000401135 <+21>:    ret
  End of assembler dump.
  (gdb) disassemble foo
  Dump of assembler code for function foo:
     0x0000000000401110 <+0>:     push   %rbp
     0x0000000000401111 <+1>:     mov    %rsp,%rbp
  ...
     0x000000000040111f <+15>:    ret
  End of assembler dump.

Note, for foo we did not get a linkage name emitted in DWARF, so
it is printed by its name:

  >> objdump --dwarf=info ./a.out | grep foo -A3 -B3
      <2b>   DW_AT_low_pc      : 0x401110
      <33>   DW_AT_high_pc     : 0x10
      <37>   DW_AT_frame_base  : 1 byte block: 56         (DW_OP_reg6 (rbp))
      <39>   DW_AT_name        : (indirect string, offset: 0x37): foo
      <3d>   DW_AT_decl_file   : 1
      <3e>   DW_AT_decl_line   : 1
      <3f>   DW_AT_prototyped  : 1

To make the macro and proc work with C++ as well, an optional argument
list was added to the regex matching the function name in the
disassemble command in function_range.  This does not change any used
behavior as currently, there exists no C++ test using the proc
function_range.

Signed-off-by: Nils-Christian Kempke <nils-christian.kempke@intel.com>
---
 gdb/testsuite/lib/dwarf.exp | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 3d833e5cd58..b5474ca6ce4 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -391,10 +391,14 @@ proc function_range { func src {options {debug}} } {
     }
 
     # Compute the size of the last instruction.
-    if { $func_length == 0 } then {
-	set func_pattern "$func"
-    } else {
-	set func_pattern "$func\\+$func_length"
+    # For C++, GDB appends arguments to the names of functions if they don't
+    # have a linkage name.  For example, asking gdb to disassemble a C++ main
+    # will print the function name as main() or main(int argc, char **argv).
+    # Take this into account by optionally allowing an argument list after
+    # the function name.
+    set func_pattern "$func\(\?\:\\(\.\*\\)\)?"
+    if { $func_length != 0 } {
+	set func_pattern "$func_pattern\\+$func_length"
     }
     set test "x/2i $func+$func_length"
     gdb_test_multiple $test $test {
-- 
2.30.2