----- Original Message -----
> Hello Dave,
>
> When using dis command on RHEL5.11, I found a weird thing. Please check the
> following execution.
>
> <cut>
> crash> dis do_wp_page | grep 591
> 0xffffffff8001115c <do_wp_page+591>: callq 0xffffffff800623d0
> <__sched_text_start>
> crash> dis schedule
> 0xffffffff800623d0 <__sched_text_start>: push %rbp
> 0xffffffff800623d1 <schedule+1>: mov %rsp,%rbp
> ...
> crash> dis do_wp_page | grep 591
> 0xffffffff8001115c <do_wp_page+591>: callq 0xffffffff800623d0 <schedule>
> crash> dis do_wp_page | grep 591
> 0xffffffff8001115c <do_wp_page+591>: callq 0xffffffff800623d0
> <__sched_text_start>
> <cut>
>
> schedule and __sched_text_start are always shifting.
>
> After some investigation, I found the following sentences in
> arch/x86_64/kernel/vmlinux.lds.S
>
> <cut>
> SECTIONS
> {
> ...
> SCHED_TEXT
> LOCK_TEXT
> KPROBES_TEXT
> ...
> <cut>
>
> the SCHED_TEXT is defined like below
> <cut>
> #define SCHED_TEXT \
> ALIGN_FUNCTION(); \
> VMLINUX_SYMBOL(__sched_text_start) = .; \
> *(.sched.text) \
> VMLINUX_SYMBOL(__sched_text_end) = .;
> <cut>
>
> So symbol __sched_text_start may have the same address as the first function
> of *(.sched.text). And LOCK_TEXT/KPROBES_TEXT/IRQENTRY_TEXT has the same
> problems. The attached patch is used to fix this.
> diff --git a/symbols.c b/symbols.c
> index cebff52..461348c 100755
> --- a/symbols.c
> +++ b/symbols.c
> @@ -4527,6 +4527,15 @@ value_search(ulong value, ulong *offset)
> (spnext->value == value))
> sp = spnext;
>
> +#define STRNVEQ(A, B) (string_exists((char *)A) && string_exists((char *)B) && \
> + strstr(A, B) && (strstr(A, B) - A) == \
> + (strlen((char *)(A)) - strlen((char *)(B))) )
> +
> + if (STRNVEQ(sp->name, "_text_start") &&
> + ((spnext = sp+1) < st->symend) &&
> + (spnext->value == value))
> + sp = spnext;
> +
> return((struct syment *)sp);
> }
> if (sp->value > value) {
Good catch -- thanks!
The "shifting" is due to the caching in symval_hash_search(). But since sp->name
is guaranteed to exist, I think the pre-existing strstr_rightmost() function makes
it a little easier to understand:
--- crash-7.0.9/symbols.c.orig
+++ crash-7.0.9/symbols.c
@@ -4527,6 +4527,11 @@ value_search(ulong value, ulong *offset)
(spnext->value == value))
sp = spnext;
+ if (strstr_rightmost(sp->name, "_text_start") &&
+ ((spnext = sp+1) < st->symend) &&
+ (spnext->value == value))
+ sp = spnext;
+
return((struct syment *)sp);
}
if (sp->value > value) {
and I'll add a comment above it.
Thanks,
Dave
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