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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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6ca6366220
This patch implements dynamic ftrace for PA-RISC. The required mcount call sequences can get pretty long, so instead of patching the whole call sequence out of the functions, we are using -fpatchable-function-entry from gcc. This puts a configurable amount of NOPS before/at the start of the function. Taking do_sys_open() as example, which would look like this when the call is patched out: 1036b248: 08 00 02 40 nop 1036b24c: 08 00 02 40 nop 1036b250: 08 00 02 40 nop 1036b254: 08 00 02 40 nop 1036b258 <do_sys_open>: 1036b258: 08 00 02 40 nop 1036b25c: 08 03 02 41 copy r3,r1 1036b260: 6b c2 3f d9 stw rp,-14(sp) 1036b264: 08 1e 02 43 copy sp,r3 1036b268: 6f c1 01 00 stw,ma r1,80(sp) When ftrace gets enabled for this function the kernel will patch these NOPs to: 1036b248: 10 19 57 20 <address of ftrace> 1036b24c: 6f c1 00 80 stw,ma r1,40(sp) 1036b250: 48 21 3f d1 ldw -18(r1),r1 1036b254: e8 20 c0 02 bv,n r0(r1) 1036b258 <do_sys_open>: 1036b258: e8 3f 1f df b,l,n .-c,r1 1036b25c: 08 03 02 41 copy r3,r1 1036b260: 6b c2 3f d9 stw rp,-14(sp) 1036b264: 08 1e 02 43 copy sp,r3 1036b268: 6f c1 01 00 stw,ma r1,80(sp) So the first NOP in do_sys_open() will be patched to jump backwards into some minimal trampoline code which pushes a stackframe, saves r1 which holds the return address, loads the address of the real ftrace function, and branches to that location. For 64 Bit things are getting a bit more complicated (and longer) because we must make sure that the address of ftrace location is 8 byte aligned, and the offset passed to ldd for fetching the address is 8 byte aligned as well. Note that gcc has a bug which misplaces the function label, and needs a patch to make dynamic ftrace work. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90751 for details. Signed-off-by: Sven Schnelle <svens@stackframe.org> Signed-off-by: Helge Deller <deller@gmx.de>
45 lines
1.0 KiB
C
45 lines
1.0 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* fixmaps for parisc
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*
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* Copyright (c) 2019 Sven Schnelle <svens@stackframe.org>
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*/
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#include <linux/kprobes.h>
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#include <linux/mm.h>
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#include <asm/cacheflush.h>
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#include <asm/fixmap.h>
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void notrace set_fixmap(enum fixed_addresses idx, phys_addr_t phys)
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{
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unsigned long vaddr = __fix_to_virt(idx);
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pgd_t *pgd = pgd_offset_k(vaddr);
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pmd_t *pmd = pmd_offset(pgd, vaddr);
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pte_t *pte;
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if (pmd_none(*pmd))
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pmd = pmd_alloc(NULL, pgd, vaddr);
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pte = pte_offset_kernel(pmd, vaddr);
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if (pte_none(*pte))
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pte = pte_alloc_kernel(pmd, vaddr);
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set_pte_at(&init_mm, vaddr, pte, __mk_pte(phys, PAGE_KERNEL_RWX));
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flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
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}
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void notrace clear_fixmap(enum fixed_addresses idx)
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{
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unsigned long vaddr = __fix_to_virt(idx);
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pgd_t *pgd = pgd_offset_k(vaddr);
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pmd_t *pmd = pmd_offset(pgd, vaddr);
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pte_t *pte = pte_offset_kernel(pmd, vaddr);
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if (WARN_ON(pte_none(*pte)))
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return;
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pte_clear(&init_mm, vaddr, pte);
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flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
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}
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