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ARM: kernel: avoid brute force search on PLT generation
Given that we now sort the relocation sections in a way that guarantees that entries that can share a single PLT entry end up adjacently, there is no a longer a need to go over the entire list to look for an existing entry that matches our jump target. If such a match exists, it was the last one to be emitted, so we can simply check the preceding slot. Note that this will still work correctly in the [theoretical] presence of call/jump relocations against SHN_UNDEF symbols with non-zero addends, although not optimally. Since the relocations are presented in the same order that we checked them for duplicates, any duplicates that we failed to spot the first time around will be accounted for in the PLT allocation so there is guaranteed to be sufficient space for them when actually emitting the PLT. For instance, the following sequence of relocations: 000004d8 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 000004fc 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 0000050e 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 00000520 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 00000532 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 00000544 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 00000556 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 00000568 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 0000057a 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 0000058c 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 0000059e 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 000005b0 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 000005c2 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null 000005d4 00058b0a R_ARM_THM_CALL 00000000 warn_slowpath_null may result in several PLT entries to be allocated, and also emitted, if any of the entries in the middle refer to a Place that contains a non-zero addend (i.e., one for all the preceding zero-addend relocations, one for all the following zero-addend relocations, and one for the non-zero addend relocation itself) Tested-by: Jongsung Kim <neidhard.kim@lge.com> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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1 changed files with 29 additions and 25 deletions
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@ -33,35 +33,39 @@ struct plt_entries {
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u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
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{
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struct plt_entries *plt, *plt_end;
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int c;
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struct plt_entries *plt = (struct plt_entries *)mod->arch.plt->sh_addr;
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int idx = 0;
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plt = (void *)mod->arch.plt->sh_addr;
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plt_end = (void *)plt + mod->arch.plt->sh_size;
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/*
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* Look for an existing entry pointing to 'val'. Given that the
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* relocations are sorted, this will be the last entry we allocated.
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* (if one exists).
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*/
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if (mod->arch.plt_count > 0) {
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plt += (mod->arch.plt_count - 1) / PLT_ENT_COUNT;
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idx = (mod->arch.plt_count - 1) % PLT_ENT_COUNT;
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/* Look for an existing entry pointing to 'val' */
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for (c = mod->arch.plt_count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) {
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int i;
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if (plt->lit[idx] == val)
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return (u32)&plt->ldr[idx];
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if (!c) {
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/* Populate a new set of entries */
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*plt = (struct plt_entries){
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{ [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
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{ val, }
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};
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mod->arch.plt_count++;
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return (u32)plt->ldr;
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}
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for (i = 0; i < PLT_ENT_COUNT; i++) {
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if (!plt->lit[i]) {
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plt->lit[i] = val;
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mod->arch.plt_count++;
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}
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if (plt->lit[i] == val)
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return (u32)&plt->ldr[i];
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}
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idx = (idx + 1) % PLT_ENT_COUNT;
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if (!idx)
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plt++;
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}
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BUG();
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mod->arch.plt_count++;
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BUG_ON(mod->arch.plt_count * PLT_ENT_SIZE > mod->arch.plt->sh_size);
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if (!idx)
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/* Populate a new set of entries */
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*plt = (struct plt_entries){
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{ [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
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{ val, }
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};
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else
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plt->lit[idx] = val;
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return (u32)&plt->ldr[idx];
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}
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#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
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