Right, but the question is whether it makes more sense to display the full slab object address containing the red-zone buffer or not. When debugging slab corruption for example, I would argue it's more relevant to show the full object address. For example, if you want to follow that linked list from kmem_cache_cpu.freelist pointer, if I'm not mistaken the next pointer in each object will be located in the first word of the object. Anyway, that is more in line with the original intent of kmem -S command, even in the case when slub debug is turned on. On the other hand, in your example above, you are presuming the address shown should be what the kmalloc() or kmem_cache_alloc() caller receives, which I agree has merit. But consider that you can enter any address within an object, and get the same result. I wonder whether there can be a compromise, such that in the case of slub debug, there could be extra information in the output display that indicates that the object contains a red zone buffer?

Hello Ogawa,

Attached is a patch for your review. You will have to enter "set redzone on" in order for the adjusted object addresses to be displayed.

diff --git a/defs.h b/defs.h index 68ed4d4..9b689b7 100644 --- a/defs.h +++ b/defs.h @@ -536,6 +536,7 @@ struct program_context { #define EXCLUDED_VMEMMAP (0x40000ULL) #define is_excluded_vmemmap() (pc->flags2 & EXCLUDED_VMEMMAP) #define MEMSRC_LOCAL (0x80000ULL) +#define REDZONE (0x100000ULL) char *cleanup; char *namelist_orig; char *namelist_debug_orig; @@ -1979,6 +1980,7 @@ struct offset_table { /* stash of commonly-used offsets */ long task_struct_stack; long tnt_mod; long radix_tree_node_shift; + long kmem_cache_red_left_pad; }; struct size_table { /* stash of commonly-used sizes */ diff --git a/help.c b/help.c index 35cd941..50b2c29 100644 --- a/help.c +++ b/help.c @@ -1072,8 +1072,12 @@ char *help_set[] = { " must be a kernel or module text address, which", " may be expressed symbolically or as a hexadecimal", " value.", -" offline show | hide Show or hide command output that is associated", +" offline show | hide show or hide command output that is associated", " with offline cpus.", +" redzone on | off if on, CONFIG_SLUB object addresses displayed by", +" the kmem command will be adjusted to reflect the", +" SLAB_RED_ZONE padding inserted at the beginning", +" of the object.", " ", " Internal variables may be set in four manners:\n", " 1. entering the set command in $HOME/.%src.", @@ -1124,6 +1128,7 @@ char *help_set[] = { " gdb: off", " scope: (not set)", " offline: show", +" redzone: off", " ", " Show the current context:\n", " %s> set", diff --git a/main.c b/main.c index 05c2042..6ab260d 100644 --- a/main.c +++ b/main.c @@ -1469,6 +1469,8 @@ dump_program_context(void) fprintf(fp, "%sSNAP", others++ ? "|" : ""); if (pc->flags2 & EXCLUDED_VMEMMAP) fprintf(fp, "%sEXCLUDED_VMEMMAP", others++ ? "|" : ""); + if (pc->flags2 & REDZONE) + fprintf(fp, "%sREDZONE", others++ ? "|" : ""); fprintf(fp, ")\n"); fprintf(fp, " namelist: %s\n", pc->namelist); diff --git a/memory.c b/memory.c index 774d090..128ed3f 100644 --- a/memory.c +++ b/memory.c @@ -723,6 +723,7 @@ vm_init(void) MEMBER_OFFSET_INIT(kmem_cache_node, "kmem_cache", "node"); MEMBER_OFFSET_INIT(kmem_cache_cpu_slab, "kmem_cache", "cpu_slab"); MEMBER_OFFSET_INIT(kmem_cache_list, "kmem_cache", "list"); + MEMBER_OFFSET_INIT(kmem_cache_red_left_pad, "kmem_cache", "red_left_pad"); MEMBER_OFFSET_INIT(kmem_cache_name, "kmem_cache", "name"); MEMBER_OFFSET_INIT(kmem_cache_flags, "kmem_cache", "flags"); MEMBER_OFFSET_INIT(kmem_cache_cpu_freelist, "kmem_cache_cpu", "freelist"); @@ -18357,6 +18358,7 @@ do_slab_slub(struct meminfo *si, int verbose) ulong freelist, cpu_freelist, cpu_slab_ptr; int i, free_objects, cpu_slab, is_free, node; ulong p, q; + ulong red_left_pad; if (!si->slab) { if (CRASHDEBUG(1)) @@ -18442,6 +18444,15 @@ do_slab_slub(struct meminfo *si, int verbose) fprintf(fp, "< SLUB: free list END (%d found) >\n", i); } + if (VALID_MEMBER(kmem_cache_red_left_pad)) { +#define SLAB_RED_ZONE 0x00000400UL + ulong flags = ULONG(si->cache_buf + OFFSET(kmem_cache_flags)); + red_left_pad = ULONG(si->cache_buf + OFFSET(kmem_cache_red_left_pad)); + if (flags & SLAB_RED_ZONE) + vaddr += red_left_pad; + } else + red_left_pad = 0; + for (p = vaddr; p < vaddr + objects * si->size; p += si->size) { hq_open(); is_free = FALSE; @@ -18482,7 +18493,8 @@ do_slab_slub(struct meminfo *si, int verbose) fprintf(fp, " %s%lx%s", is_free ? " " : "[", - p, is_free ? " " : "]"); + pc->flags2 & REDZONE ? p : p - red_left_pad, + is_free ? " " : "]"); if (is_free && (cpu_slab >= 0)) fprintf(fp, "(cpu %d cache)", cpu_slab); fprintf(fp, "\n"); diff --git a/symbols.c b/symbols.c index c6d1a6a..1d8dd13 100644 --- a/symbols.c +++ b/symbols.c @@ -9332,6 +9332,8 @@ dump_offset_table(char *spec, ulong makestruct) OFFSET(kmem_cache_name)); fprintf(fp, " kmem_cache_list: %ld\n", OFFSET(kmem_cache_list)); + fprintf(fp, " kmem_cache_red_left_pad: %ld\n", + OFFSET(kmem_cache_red_left_pad)); fprintf(fp, " kmem_cache_node: %ld\n", OFFSET(kmem_cache_node)); fprintf(fp, " kmem_cache_cpu_slab: %ld\n", diff --git a/tools.c b/tools.c index 494af07..01b52cd 100644 --- a/tools.c +++ b/tools.c @@ -2435,6 +2435,31 @@ cmd_set(void) return; + } else if (STREQ(args[optind], "redzone")) { + if (args[optind+1]) { + optind++; + if (STREQ(args[optind], "on")) + pc->flags2 |= REDZONE; + else if (STREQ(args[optind], "off")) + pc->flags2 &= ~REDZONE; + else if (IS_A_NUMBER(args[optind])) { + value = stol(args[optind], + FAULT_ON_ERROR, NULL); + if (value) + pc->flags2 |= REDZONE; + else + pc->flags2 &= ~REDZONE; + } else + goto invalid_set_command; + } + + if (runtime) { + fprintf(fp, "redzone: %s\n", + pc->flags2 & REDZONE ? + "on" : "off"); + } + return; + } else if (XEN_HYPER_MODE()) { error(FATAL, "invalid argument for the Xen hypervisor\n"); } else if (pc->flags & MINIMAL_MODE) { @@ -2541,6 +2566,7 @@ show_options(void) else fprintf(fp, "(not set)\n"); fprintf(fp, " offline: %s\n", pc->flags2 & OFFLINE_HIDE ? "hide" : "show"); + fprintf(fp, " redzone: %s\n", pc->flags2 & REDZONE ? "on" : "off"); }