[gdb/testsuite] Fix gdb.arch/amd64-stap-three-arg-disp.S

On SLE-11 I ran into:
...
(gdb) print $_probe_arg0^M
Cannot access memory at address 0x8000003fe05c^M
(gdb) FAIL: gdb.arch/amd64-stap-special-operands.exp: probe: three_arg: \
  print $_probe_arg0
...

The memory cannot be accessed because the address used to evaluate
$_probe_arg0 at the probe point is incorrect.

The address is calculated using this expression:
...
.asciz "-4@-4(%rbp,%ebx,0)"
...
which uses $ebx, but $ebx is uninitialized at the probe point.

The test-case does contain a "movl $0, %ebx" insn to set $ebx to 0, but that
insn is placed after the probe point.  We could fix this by moving the insn
to before the probe point.  But, $ebx is also a callee-save register, so
normally, if we modify it, we also need to save and restore it, which is
currently not done.  This is currently not harmful, because we don't run the
test-case further than the probe point, but it's bound to cause confusion.

So, fix this instead by using $eax instead in the expression, and moving the
insn setting $eax to 0 to before the probe point.

gdb/testsuite/ChangeLog:

2021-01-11  Tom de Vries  <tdevries@suse.de>

	PR testsuite/26968
	* gdb.arch/amd64-stap-three-arg-disp.S: Remove insn modifying $ebx.
	Move insn setting $eax to before probe point.

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 03593c5499e01d2cca52fb0ec08fc848e7ac6b0e..65bbebfb598b751718618b8b573147c7fab3e595 100644 (file)
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2021-01-11  Tom de Vries  <tdevries@suse.de>
+
+       PR testsuite/26968
+       * gdb.arch/amd64-stap-three-arg-disp.S: Remove insn modifying $ebx.
+       Move insn setting $eax to before probe point.
+
 2021-01-09  Tom Tromey  <tom@tromey.com>
 
        * gdb.trace/ax.exp: Do not require an "ext".

diff --git a/gdb/testsuite/gdb.arch/amd64-stap-three-arg-disp.S b/gdb/testsuite/gdb.arch/amd64-stap-three-arg-disp.S
index cf3856f41e982f5e6197ae7f5fd438d93a50b735..17b640480821ac0584483d911f32c0c76f9591b5 100644 (file)
--- a/gdb/testsuite/gdb.arch/amd64-stap-three-arg-disp.S
+++ b/gdb/testsuite/gdb.arch/amd64-stap-three-arg-disp.S
@@ -15,6 +15,7 @@ main:
        movl    %edi, -20(%rbp)
        movq    %rsi, -32(%rbp)
        movl    $10, -4(%rbp)
+       movl    $0, %eax
 #APP
 # 8 "amd64-stap-three-arg-disp.c" 1
        990: nop
@@ -28,7 +29,7 @@ main:
 .8byte 0
 .asciz "test"
 .asciz "three_arg"
-.asciz "-4@-4(%rbp,%ebx,0)"
+.asciz "-4@-4(%rbp,%eax,0)"
 994: .balign 4
 .popsection
 
@@ -45,8 +46,6 @@ _.stapsdt.base: .space 1
 
 # 0 "" 2
 #NO_APP
-       movl    $0, %eax
-       movl    $0, %ebx
        popq    %rbp
        .cfi_def_cfa 7, 8
 # SUCC: EXIT [100.0%]