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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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091283e3d5
[ Upstream commit 3cb17cce1e76ccc5499915a4d7e095a1ad6bf7ff ]
If we just check whether the variable can be converted, 'tvar' should be
a null pointer. However, the null pointer check is missing in the
'Constant value' execution path.
The following cases can trigger this problem:
$ cat test.c
#include <stdio.h>
void main(void)
{
int a;
const int b = 1;
asm volatile("mov %1, %0" : "=r"(a): "i"(b));
printf("a: %d\n", a);
}
$ gcc test.c -o test -O -g
$ sudo ./perf probe -x ./test -L "main"
<main@/home/lhf/test.c:0>
0 void main(void)
{
2 int a;
const int b = 1;
asm volatile("mov %1, %0" : "=r"(a): "i"(b));
6 printf("a: %d\n", a);
}
$ sudo ./perf probe -x ./test -V "main:6"
Segmentation fault
The check on 'tvar' is added. If 'tavr' is a null pointer, we return 0
to indicate that the variable can be converted. Now, we can successfully
show the variables that can be accessed.
$ sudo ./perf probe -x ./test -V "main:6"
Available variables at main:6
@<main+13>
char* __fmt
int a
int b
However, the variable 'b' cannot be tracked.
$ sudo ./perf probe -x ./test -D "main:6 b"
Failed to find the location of the 'b' variable at this address.
Perhaps it has been optimized out.
Use -V with the --range option to show 'b' location range.
Error: Failed to add events.
This is because __die_find_variable_cb() did not successfully match
variable 'b', which has the DW_AT_const_value attribute instead of
DW_AT_location. We added support for DW_AT_const_value in
__die_find_variable_cb(). With this modification, we can successfully
track the variable 'b'.
$ sudo ./perf probe -x ./test -D "main:6 b"
p:probe_test/main_L6 /home/lhf/test:0x1156 b=\1:s32
Fixes:
|
||
|---|---|---|
| .. | ||
| arch | ||
| bench | ||
| Documentation | ||
| examples/bpf | ||
| include/bpf | ||
| jvmti | ||
| pmu-events | ||
| python | ||
| scripts | ||
| tests | ||
| trace | ||
| ui | ||
| util | ||
| .gitignore | ||
| Build | ||
| builtin-annotate.c | ||
| builtin-bench.c | ||
| builtin-buildid-cache.c | ||
| builtin-buildid-list.c | ||
| builtin-c2c.c | ||
| builtin-config.c | ||
| builtin-data.c | ||
| builtin-diff.c | ||
| builtin-evlist.c | ||
| builtin-ftrace.c | ||
| builtin-help.c | ||
| builtin-inject.c | ||
| builtin-kallsyms.c | ||
| builtin-kmem.c | ||
| builtin-kvm.c | ||
| builtin-list.c | ||
| builtin-lock.c | ||
| builtin-mem.c | ||
| builtin-probe.c | ||
| builtin-record.c | ||
| builtin-report.c | ||
| builtin-sched.c | ||
| builtin-script.c | ||
| builtin-stat.c | ||
| builtin-timechart.c | ||
| builtin-top.c | ||
| builtin-trace.c | ||
| builtin-version.c | ||
| builtin.h | ||
| check-headers.sh | ||
| command-list.txt | ||
| CREDITS | ||
| design.txt | ||
| Makefile | ||
| Makefile.config | ||
| Makefile.perf | ||
| MANIFEST | ||
| perf-archive.sh | ||
| perf-completion.sh | ||
| perf-read-vdso.c | ||
| perf-sys.h | ||
| perf-with-kcore.sh | ||
| perf.c | ||
| perf.h | ||