[Crash-utility] [PATCH] Fix for 4.19-rc1 and later "relative __ksymtab entries"
Dave Anderson
anderson at redhat.com
Wed Aug 29 14:46:47 UTC 2018
----- Original Message -----
> kernels which have CONFIG_HAVE_ARCH_PREL32_RELOCATIONS will now store
> module symbol values relative to themselves since linux kernel's commit
> 7290d580957 ("module: use relative references for __ksymtab entries")
>
> Do the lookup one way or another depending on the kernel's kernel_symbol
> struct, the case without the ARCH_PREL32_RELOCATIONS is the same as the
> old behaviour
Hi Dominique,
Thanks for both the bug report and fix -- your patch is queued for crash-7.2.4:
https://github.com/crash-utility/crash/commit/001f77a05585c15ebd14bb72d5fde314a63c06fe
My task_struct.pids patch has also been applied:
https://github.com/crash-utility/crash/commit/d7eec45d4c2cdd836ce48a81b0ae688a7d2879ba
Thanks,
Dave
>
> ---
> Hi! This is a follow-up on the bz I opened yesterday[1]
>
> I'll let you commit your part of the tasks_struct pids, with both patches
> I can start crash normally and could check that address of symbols within
> a module look correct when compared to /proc/kallsyms, so I guess this
> isn't too bad.
> I also tried with an older kernel without problem.
>
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1623127
>
> defs.h | 1 +
> symbols.c | 98 +++++++++++++++++++++++++++++++++++++------------------
> 2 files changed, 68 insertions(+), 31 deletions(-)
>
> diff --git a/defs.h b/defs.h
> index 8687ff1..166ee48 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -2036,6 +2036,7 @@ struct offset_table { /* stash of
> commonly-used offsets */
> long memcg_cache_params___root_caches_node;
> long memcg_cache_params_children;
> long memcg_cache_params_children_node;
> + long kernel_symbol_value;
> };
>
> struct size_table { /* stash of commonly-used sizes */
> diff --git a/symbols.c b/symbols.c
> index 2e6713a..7e73bad 100644
> --- a/symbols.c
> +++ b/symbols.c
> @@ -1595,12 +1595,40 @@ store_module_symbols_v1(ulong total, int
> mods_installed)
> st->flags |= INSMOD_BUILTIN;
> }
>
> -struct kernel_symbol
> -{
> - unsigned long value;
> - const char *name;
> +union kernel_symbol {
> + struct kernel_symbol_v1 {
> + unsigned long value;
> + const char *name;
> + } v1;
> + /* kernel 4.19 introduced relative symbol positionning */
> + struct kernel_symbol_v2 {
> + int value_offset;
> + int name_offset;
> + } v2;
> };
>
> +static ulong
> +modsym_name(ulong syms, union kernel_symbol *modsym, int i)
> +{
> + if (VALID_MEMBER(kernel_symbol_value))
> + return (ulong)modsym->v1.name;
> +
> + return syms + i * sizeof(struct kernel_symbol_v2) +
> + offsetof(struct kernel_symbol_v2, name_offset) +
> + modsym->v2.name_offset;
> +}
> +
> +static ulong
> +modsym_value(ulong syms, union kernel_symbol *modsym, int i)
> +{
> + if (VALID_MEMBER(kernel_symbol_value))
> + return (ulong)modsym->v1.value;
> +
> + return syms + i * sizeof(struct kernel_symbol_v2) +
> + offsetof(struct kernel_symbol_v2, value_offset) +
> + modsym->v2.value_offset;
> +}
> +
> void
> store_module_symbols_v2(ulong total, int mods_installed)
> {
> @@ -1614,7 +1642,8 @@ store_module_symbols_v2(ulong total, int
> mods_installed)
> long strbuflen;
> ulong size;
> int mcnt, lm_mcnt;
> - struct kernel_symbol *modsym;
> + union kernel_symbol *modsym;
> + size_t kernel_symbol_size;
> struct load_module *lm;
> char buf1[BUFSIZE];
> char buf2[BUFSIZE];
> @@ -1639,6 +1668,13 @@ store_module_symbols_v2(ulong total, int
> mods_installed)
> "re-initialization of module symbols not implemented yet!\n");
> }
>
> + MEMBER_OFFSET_INIT(kernel_symbol_value, "kernel_symbol", "value");
> + if (VALID_MEMBER(kernel_symbol_value)) {
> + kernel_symbol_size = sizeof(struct kernel_symbol_v1);
> + } else {
> + kernel_symbol_size = sizeof(struct kernel_symbol_v2);
> + }
> +
> if ((st->ext_module_symtable = (struct syment *)
> calloc(total, sizeof(struct syment))) == NULL)
> error(FATAL, "v2 module syment space malloc (%ld symbols):
> %s\n",
> @@ -1750,20 +1786,20 @@ store_module_symbols_v2(ulong total, int
> mods_installed)
> }
>
> if (nsyms) {
> - modsymbuf = GETBUF(sizeof(struct kernel_symbol)*nsyms);
> + modsymbuf = GETBUF(kernel_symbol_size*nsyms);
> readmem((ulong)syms, KVADDR, modsymbuf,
> - nsyms * sizeof(struct kernel_symbol),
> + nsyms * kernel_symbol_size,
> "module symbols", FAULT_ON_ERROR);
> }
>
> for (i = first = last = 0; i < nsyms; i++) {
> - modsym = (struct kernel_symbol *)
> - (modsymbuf + (i * sizeof(struct kernel_symbol)));
> + modsym = (union kernel_symbol *)
> + (modsymbuf + (i * kernel_symbol_size));
> if (!first
> - || first > (ulong)modsym->name)
> - first = (ulong)modsym->name;
> - if ((ulong)modsym->name > last)
> - last = (ulong)modsym->name;
> + || first > modsym_name(syms, modsym, i))
> + first = modsym_name(syms, modsym, i);
> + if (modsym_name(syms, modsym, i) > last)
> + last = modsym_name(syms, modsym, i);
> }
>
> if (last > first) {
> @@ -1787,21 +1823,21 @@ store_module_symbols_v2(ulong total, int
> mods_installed)
>
> for (i = 0; i < nsyms; i++) {
>
> - modsym = (struct kernel_symbol *)
> - (modsymbuf + (i * sizeof(struct kernel_symbol)));
> + modsym = (union kernel_symbol *)
> + (modsymbuf + (i * kernel_symbol_size));
>
> BZERO(buf1, BUFSIZE);
>
> if (strbuf)
> strcpy(buf1,
> - &strbuf[(ulong)modsym->name - first]);
> + &strbuf[modsym_name(syms, modsym, i) - first]);
> else
> - read_string((ulong)modsym->name, buf1,
> + read_string(modsym_name(syms, modsym, i), buf1,
> BUFSIZE-1);
>
> if (strlen(buf1)) {
> st->ext_module_symtable[mcnt].value =
> - modsym->value;
> + modsym_value(syms, modsym, i);
> st->ext_module_symtable[mcnt].type = '?';
> st->ext_module_symtable[mcnt].flags |= MODULE_SYMBOL;
> strip_module_symbol_end(buf1);
> @@ -1823,21 +1859,21 @@ store_module_symbols_v2(ulong total, int
> mods_installed)
> FREEBUF(strbuf);
>
> if (ngplsyms) {
> - modsymbuf = GETBUF(sizeof(struct kernel_symbol) *
> + modsymbuf = GETBUF(kernel_symbol_size *
> ngplsyms);
> readmem((ulong)gpl_syms, KVADDR, modsymbuf,
> - ngplsyms * sizeof(struct kernel_symbol),
> + ngplsyms * kernel_symbol_size,
> "module gpl symbols", FAULT_ON_ERROR);
> }
>
> for (i = first = last = 0; i < ngplsyms; i++) {
> - modsym = (struct kernel_symbol *)
> - (modsymbuf + (i * sizeof(struct kernel_symbol)));
> + modsym = (union kernel_symbol *)
> + (modsymbuf + (i * kernel_symbol_size));
> if (!first
> - || first > (ulong)modsym->name)
> - first = (ulong)modsym->name;
> - if ((ulong)modsym->name > last)
> - last = (ulong)modsym->name;
> + || first > modsym_name(gpl_syms, modsym, i))
> + first = modsym_name(gpl_syms, modsym, i);
> + if (modsym_name(gpl_syms, modsym, i) > last)
> + last = modsym_name(gpl_syms, modsym, i);
> }
>
> if (last > first) {
> @@ -1860,21 +1896,21 @@ store_module_symbols_v2(ulong total, int
> mods_installed)
>
> for (i = 0; i < ngplsyms; i++) {
>
> - modsym = (struct kernel_symbol *)
> - (modsymbuf + (i * sizeof(struct kernel_symbol)));
> + modsym = (union kernel_symbol *)
> + (modsymbuf + (i * kernel_symbol_size));
>
> BZERO(buf1, BUFSIZE);
>
> if (strbuf)
> strcpy(buf1,
> - &strbuf[(ulong)modsym->name - first]);
> + &strbuf[modsym_name(gpl_syms, modsym, i) - first]);
> else
> - read_string((ulong)modsym->name, buf1,
> + read_string(modsym_name(gpl_syms, modsym, i), buf1,
> BUFSIZE-1);
>
> if (strlen(buf1)) {
> st->ext_module_symtable[mcnt].value =
> - modsym->value;
> + modsym_value(gpl_syms, modsym, i);
> st->ext_module_symtable[mcnt].type = '?';
> st->ext_module_symtable[mcnt].flags |= MODULE_SYMBOL;
> strip_module_symbol_end(buf1);
> --
> 2.17.1
>
> --
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