![Sven Schnelle](/assets/img/avatar_default.png)
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>
188 lines
3.9 KiB
ArmAsm
188 lines
3.9 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/* Kernel link layout for various "sections"
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*
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* Copyright (C) 1999-2003 Matthew Wilcox <willy at parisc-linux.org>
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* Copyright (C) 2000-2003 Paul Bame <bame at parisc-linux.org>
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* Copyright (C) 2000 John Marvin <jsm at parisc-linux.org>
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* Copyright (C) 2000 Michael Ang <mang with subcarrier.org>
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* Copyright (C) 2002 Randolph Chung <tausq with parisc-linux.org>
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* Copyright (C) 2003 James Bottomley <jejb with parisc-linux.org>
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* Copyright (C) 2006-2013 Helge Deller <deller@gmx.de>
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*/
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/*
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* Put page table entries (swapper_pg_dir) as the first thing in .bss. This
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* will ensure that it has .bss alignment (PAGE_SIZE).
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*/
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#define BSS_FIRST_SECTIONS *(.data..vm0.pmd) \
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*(.data..vm0.pgd) \
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*(.data..vm0.pte)
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#define CC_USING_PATCHABLE_FUNCTION_ENTRY
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#include <asm-generic/vmlinux.lds.h>
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/* needed for the processor specific cache alignment size */
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#include <asm/cache.h>
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#include <asm/page.h>
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#include <asm/asm-offsets.h>
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#include <asm/thread_info.h>
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/* ld script to make hppa Linux kernel */
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#ifndef CONFIG_64BIT
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OUTPUT_FORMAT("elf32-hppa-linux")
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OUTPUT_ARCH(hppa)
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#else
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OUTPUT_FORMAT("elf64-hppa-linux")
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OUTPUT_ARCH(hppa:hppa2.0w)
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#endif
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#define EXIT_TEXT_SECTIONS() .exit.text : { EXIT_TEXT }
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#if !defined(CONFIG_64BIT) || defined(CONFIG_MLONGCALLS)
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#define MLONGCALL_KEEP(x)
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#define MLONGCALL_DISCARD(x) x
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#else
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#define MLONGCALL_KEEP(x) x
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#define MLONGCALL_DISCARD(x)
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#endif
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ENTRY(parisc_kernel_start)
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#ifndef CONFIG_64BIT
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jiffies = jiffies_64 + 4;
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#else
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jiffies = jiffies_64;
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#endif
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SECTIONS
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{
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. = KERNEL_BINARY_TEXT_START;
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__init_begin = .;
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HEAD_TEXT_SECTION
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MLONGCALL_DISCARD(INIT_TEXT_SECTION(8))
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. = ALIGN(PAGE_SIZE);
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INIT_DATA_SECTION(PAGE_SIZE)
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MLONGCALL_DISCARD(EXIT_TEXT_SECTIONS())
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.exit.data :
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{
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EXIT_DATA
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}
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PERCPU_SECTION(8)
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. = ALIGN(4);
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.altinstructions : {
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__alt_instructions = .;
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*(.altinstructions)
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__alt_instructions_end = .;
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}
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. = ALIGN(HUGEPAGE_SIZE);
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__init_end = .;
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/* freed after init ends here */
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_text = .; /* Text and read-only data */
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_stext = .;
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MLONGCALL_KEEP(INIT_TEXT_SECTION(8))
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.text ALIGN(PAGE_SIZE) : {
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TEXT_TEXT
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LOCK_TEXT
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SCHED_TEXT
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CPUIDLE_TEXT
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KPROBES_TEXT
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IRQENTRY_TEXT
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SOFTIRQENTRY_TEXT
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*(.text.do_softirq)
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*(.text.sys_exit)
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*(.text.do_sigaltstack)
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*(.text.do_fork)
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*(.text.div)
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*($$*) /* millicode routines */
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*(.text.*)
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*(.fixup)
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*(.lock.text) /* out-of-line lock text */
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*(.gnu.warning)
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}
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MLONGCALL_KEEP(EXIT_TEXT_SECTIONS())
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. = ALIGN(PAGE_SIZE);
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_etext = .;
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/* End of text section */
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/* Start of data section */
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_sdata = .;
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/* Architecturally we need to keep __gp below 0x1000000 and thus
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* in front of RO_DATA_SECTION() which stores lots of tracepoint
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* and ftrace symbols. */
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#ifdef CONFIG_64BIT
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. = ALIGN(16);
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/* Linkage tables */
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.opd : {
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__start_opd = .;
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*(.opd)
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__end_opd = .;
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} PROVIDE (__gp = .);
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.plt : {
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*(.plt)
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}
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.dlt : {
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*(.dlt)
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}
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#endif
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RO_DATA_SECTION(8)
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/* RO because of BUILDTIME_EXTABLE_SORT */
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EXCEPTION_TABLE(8)
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NOTES
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/* unwind info */
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.PARISC.unwind : {
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__start___unwind = .;
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*(.PARISC.unwind)
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__stop___unwind = .;
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}
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/* writeable */
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/* Make sure this is page aligned so
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* that we can properly leave these
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* as writable
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*/
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. = ALIGN(HUGEPAGE_SIZE);
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data_start = .;
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/* Data */
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RW_DATA_SECTION(L1_CACHE_BYTES, PAGE_SIZE, PAGE_SIZE)
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/* PA-RISC locks requires 16-byte alignment */
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. = ALIGN(16);
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.data..lock_aligned : {
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*(.data..lock_aligned)
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}
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/* End of data section */
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_edata = .;
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/* BSS */
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BSS_SECTION(PAGE_SIZE, PAGE_SIZE, PAGE_SIZE)
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. = ALIGN(HUGEPAGE_SIZE);
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_end = . ;
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STABS_DEBUG
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.note 0 : { *(.note) }
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/* Sections to be discarded */
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DISCARDS
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/DISCARD/ : {
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#ifdef CONFIG_64BIT
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/* temporary hack until binutils is fixed to not emit these
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* for static binaries
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*/
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*(.interp)
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*(.dynsym)
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*(.dynstr)
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*(.dynamic)
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*(.hash)
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*(.gnu.hash)
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#endif
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}
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}
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