[PATCH v2] gdb/record: avoid rax usage in i386-avx-record.exp

[PATCH v2] gdb/record: avoid rax usage in i386-avx-record.exp

[Guinevere Larsen]

My recent commit, 1c04308f0958cbac83bad22703758139ea6969b6:

    Author: Guinevere Larsen <guinevere@redhat.com>
    Date:   Tue Jun 16 16:03:43 2026 -0300
    gdb/record: add support for BMI2 instructions

Introduced a few tests that rely on the rax register being set before
entering the function. This isn't reliable, as programs compiled with
gcc-14 and earlier will have the register. To avoid compiler versions
getting in the way, this commit changes the test to use r12 (and
r12w/r12d when appropriate).

Reported-by: Christina Joos <christina.joos@intel.com>
Reviewed-by: Christina Joos <christina.joos@intel.com>
---
 gdb/testsuite/gdb.reverse/i386-avx-reverse.c  | 32 +++++++++----------
 .../gdb.reverse/i386-avx-reverse.exp          |  8 ++---
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/gdb/testsuite/gdb.reverse/i386-avx-reverse.c b/gdb/testsuite/gdb.reverse/i386-avx-reverse.c
index 88cd3fc7f34..4d45482c07a 100644
--- a/gdb/testsuite/gdb.reverse/i386-avx-reverse.c
+++ b/gdb/testsuite/gdb.reverse/i386-avx-reverse.c
@@ -770,48 +770,48 @@ bmi_test ()
 {
   /* start bmi_test.  */
   /* Using GDB, load these values onto registers for testing.
-     eax = 0x1312
+     r12 = 0x1312
      ebx = 0xdeadbeef
      ecx = 0xcafeface
      edx = 0x2337
      r8  = 0
      this way it's easy to confirm we're undoing things correctly.  */
 
-  asm volatile ("andn %rbx, %rax, %r8");
-  asm volatile ("andn %ebx, %eax, %ecx");
+  asm volatile ("andn %rbx, %r12, %r8");
+  asm volatile ("andn %ebx, %r12d, %ecx");
 
   asm volatile ("bextr %rcx, %r8, %rbx");
   asm volatile ("bextr %ebx, %ecx, %r8d");
 
-  asm volatile ("blsi %rax, %rcx");
+  asm volatile ("blsi %r12, %rcx");
   asm volatile ("blsi %ebx, %r8d");
 
   asm volatile ("blsmsk %r8, %rbx");
-  asm volatile ("blsmsk %eax, %eax");
+  asm volatile ("blsmsk %r12d, %r12d");
 
   asm volatile ("blsr %rcx, %rbx");
   asm volatile ("blsr %r8d, %ecx");
 
-  asm volatile ("lzcnt %rax, %r8");
-  asm volatile ("lzcnt %eax, %ecx");
-  asm volatile ("lzcnt %ax, %bx");
+  asm volatile ("lzcnt %r12, %r8");
+  asm volatile ("lzcnt %r12d, %ecx");
+  asm volatile ("lzcnt %r12w, %bx");
 
-  asm volatile ("tzcnt %rax, %rcx");
-  asm volatile ("tzcnt %eax, %ebx");
-  asm volatile ("tzcnt %ax, %r8w");
+  asm volatile ("tzcnt %r12, %rcx");
+  asm volatile ("tzcnt %r12d, %ebx");
+  asm volatile ("tzcnt %r12w, %r8w");
 
-  asm volatile ("mulx %eax, %ebx, %ecx");
+  asm volatile ("mulx %r12d, %ebx, %ecx");
   asm volatile ("mulx %ebx, %ecx, %ebx");
 
   asm volatile ("pdep %r8, %rcx, %rbx");
   asm volatile ("pext %edx, %ecx, %ebx");
   asm volatile ("rorx $10, %r8, %rbx");
-  asm volatile ("sarx %edx, %ebx, %eax");
-  asm volatile ("shlx %eax, %ecx, %ebx");
-  asm volatile ("shrx %r8d, %eax, %ecx");
+  asm volatile ("sarx %edx, %ebx, %r12d");
+  asm volatile ("shlx %r12d, %ecx, %ebx");
+  asm volatile ("shrx %r8d, %r12d, %ecx");
 
   asm volatile ("bzhi %edx, %ebx, %r8d");
-  asm volatile ("bzhi %rax, %rcx, %r8");
+  asm volatile ("bzhi %r12, %rcx, %r8");
 
   return 0; /* end bmi_test  */
 }
diff --git a/gdb/testsuite/gdb.reverse/i386-avx-reverse.exp b/gdb/testsuite/gdb.reverse/i386-avx-reverse.exp
index 5d65245db39..a5b0e6612aa 100644
--- a/gdb/testsuite/gdb.reverse/i386-avx-reverse.exp
+++ b/gdb/testsuite/gdb.reverse/i386-avx-reverse.exp
@@ -1201,7 +1201,7 @@ gdb_test "finish" "Run till exit from.*convert_test.*" \
 gdb_test_no_output \
     "set \$r8 = 0" "set r8 for bmi test"
 gdb_test_no_output \
-    "set \$eax = 0x1312" "set eax for bmi test"
+    "set \$r12 = 0x1312" "set r12 for bmi test"
 gdb_test_no_output "set \$ebx = 0xdeadbeef" "set ebx for bmi test"
 gdb_test_no_output "set \$ecx = 0xcafeface" "set ecx for bmi test"
 gdb_test_no_output "set \$edx = 0x2337" "set edx for bmi test"
@@ -1213,7 +1213,7 @@ if {[record_full_function "bmi"] == true} {
 
     test_one_general_register "shrx" "ecx" "0xe884173"
     test_one_general_register "shlx" "ebx" "0x0"
-    test_one_general_register "sarx" "eax" "0x3"
+    test_one_general_register "sarx" "r12" "0x3"
     test_one_general_register "rorx" "ebx" "0x3b"
     test_one_general_register "pext" "ebx" "0x0"
     test_one_general_register "pdep" "ebx" "0x0"
@@ -1232,13 +1232,13 @@ if {[record_full_function "bmi"] == true} {
     test_one_general_register "blsr" "ecx" "0x2"
     test_one_general_register "blsr" "ebx" "0xffffffff"
 
-    test_one_general_register "blsmsk" "eax" "0x1312"
+    test_one_general_register "blsmsk" "r12" "0x1312"
     test_one_general_register "blsmsk" "ebx" "0x0"
 
     test_one_general_register "blsi" "r8" "0x0"
     test_one_general_register "blsi" "ecx" "0xdeadaced"
 
-    test_one_general_register "bextr" "eax" "0x1312"
+    test_one_general_register "bextr" "r12" "0x1312"
     test_one_general_register "bextr" "ebx" "0xdeadbeef"
 
     test_one_general_register "andn" "ecx" "0xcafeface"

base-commit: a80fede20bc1330eca5e419392c6595bb3a6ac1d
-- 
2.55.0

Re: [PATCH v2] gdb/record: avoid rax usage in i386-avx-record.exp

[Simon Marchi]

On 8/13/26 9:10 AM, Guinevere Larsen wrote:
> My recent commit, 1c04308f0958cbac83bad22703758139ea6969b6:
> 
>     Author: Guinevere Larsen <guinevere@redhat.com>
>     Date:   Tue Jun 16 16:03:43 2026 -0300
>     gdb/record: add support for BMI2 instructions
> 
> Introduced a few tests that rely on the rax register being set before
> entering the function. This isn't reliable, as programs compiled with
> gcc-14 and earlier will have the register. To avoid compiler versions

This sentence ends abruptly.

It's not clear to me what the problem is, could you explain it in simple
words :)?

Simon

Re: [PATCH v2] gdb/record: avoid rax usage in i386-avx-record.exp

[Guinevere Larsen]

On 8/13/26 11:51 AM, Simon Marchi wrote:
> On 8/13/26 9:10 AM, Guinevere Larsen wrote:
>> My recent commit, 1c04308f0958cbac83bad22703758139ea6969b6:
>>
>>      Author: Guinevere Larsen <guinevere@redhat.com>
>>      Date:   Tue Jun 16 16:03:43 2026 -0300
>>      gdb/record: add support for BMI2 instructions
>>
>> Introduced a few tests that rely on the rax register being set before
>> entering the function. This isn't reliable, as programs compiled with
>> gcc-14 and earlier will have the register. To avoid compiler versions
> This sentence ends abruptly.
>
> It's not clear to me what the problem is, could you explain it in simple
> words :)?
>
> Simon
>
oops, sorry, need to do more proofreading I guess. The sentence should 
be "will have the registered clobbered, saving 0 on it"

I haven't looked at the disassembly to know why, but something about how 
GCC 14 encodes the function calls makes EAX be 0 every time, and the 
test expects eax to be something else. Moving to a different register 
sidesteps this

-- 
Cheers,
Guinevere Larsen
it/its
she/her (deprecated)