[pushed,1/2,gdb/testsuite] Make gdb.base/longjmp.exp FAIL more stable across archs
Commit Message
When running test-case gdb.base/longjmp.exp on x86_64-linux, the master
longjmp breakpoint is set using probes and the test-case passes:
...
(gdb) PASS: gdb.base/longjmp.exp: next to longjmp (1)
next^M
0x00000000004005cc 49 if (setjmp (env) == 0) /* patt1 */^M
(gdb) PASS: gdb.base/longjmp.exp: next over longjmp(1)
next^M
56 resumes++;^M
(gdb) PASS: gdb.base/longjmp.exp: next into else block (1)
...
However, if I disable
create_longjmp_master_breakpoint_probe, we have instead:
...
(gdb) PASS: gdb.base/longjmp.exp: next to longjmp (1)
next^M
56 resumes++;^M
(gdb) FAIL: gdb.base/longjmp.exp: next over longjmp(1)
...
At first glance, the failure mode doesn't look too bad: we stop
a few insns later than the passing scenario.
For contrast, if we do the same on powerpc64le, the failure mode is:
...
(gdb) PASS: gdb.base/longjmp.exp: next to longjmp (1)
next^M
^M
Breakpoint 3, main () at longjmp.c:59^M
59 i = 1; /* miss_step_1 */^M
(gdb) FAIL: gdb.base/longjmp.exp: next over longjmp(1)
...
Here we only stop because of running into the safety net breakpoint at
miss_step_1.
So, how does this happen on x86_64? Let's look at the code:
...
4005c7: e8 94 fe ff ff call 400460 <_setjmp@plt>
4005cc: 85 c0 test %eax,%eax
4005ce: 75 1e jne 4005ee <main+0x3b>
4005d0: 8b 05 8e 0a 20 00 mov 0x200a8e(%rip),%eax # 601064 <longjmps>
4005d6: 83 c0 01 add $0x1,%eax
4005d9: 89 05 85 0a 20 00 mov %eax,0x200a85(%rip) # 601064 <longjmps>
4005df: be 01 00 00 00 mov $0x1,%esi
4005e4: bf 80 10 60 00 mov $0x601080,%edi
4005e9: e8 82 fe ff ff call 400470 <longjmp@plt>
4005ee: 8b 05 74 0a 20 00 mov 0x200a74(%rip),%eax # 601068 <resumes>
...
The next over the longjmp call at 4005e9 is supposed to stop at the longjmp
target at 4005cc, but instead we stop at 4005ee, where we have the step-resume
breakpoint inserted by the next. In other words, we accidentally "return"
from the longjmp call to the insn immediately after it (even though
a longjmp is a noreturn function).
Try to avoid this accident and make the failure mode on x86_64 the same as on
powerpc64le, by switching the then and else branch.
Tested on x86_64-linux.
---
gdb/testsuite/gdb.base/longjmp.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
base-commit: c8ea5e409b02cf7fa848e44af74b2e8246ad03f1
@@ -46,14 +46,14 @@ main ()
volatile int i = 0;
/* Pattern 1 - simple longjmp. */
- if (setjmp (env) == 0) /* patt1 */
+ if (setjmp (env) != 0) /* patt1 */
{
- longjmps++;
- longjmp (env, 1);
+ resumes++;
}
else
{
- resumes++;
+ longjmps++;
+ longjmp (env, 1);
}
i = 1; /* miss_step_1 */