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author | Sven Schnelle <svens@stackframe.org> | 2019-06-05 22:32:22 +0200 |
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committer | Helge Deller <deller@gmx.de> | 2019-06-08 12:56:29 +0200 |
commit | 6ca6366220ed285e29ee22f4cf5c68a0397cb005 (patch) | |
tree | e6ba9bb5f0eeab4e10205cbb479189237bee72c1 /include/asm-generic/vmlinux.lds.h | |
parent | 2809b392a62ae307da058a52d451b2fc3ce4de7e (diff) | |
download | linux-stable-6ca6366220ed285e29ee22f4cf5c68a0397cb005.tar.gz linux-stable-6ca6366220ed285e29ee22f4cf5c68a0397cb005.tar.bz2 linux-stable-6ca6366220ed285e29ee22f4cf5c68a0397cb005.zip |
parisc: add dynamic ftrace
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>
Diffstat (limited to 'include/asm-generic/vmlinux.lds.h')
-rw-r--r-- | include/asm-generic/vmlinux.lds.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 088987e9a3ea..ca42182992a5 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -110,10 +110,17 @@ #endif #ifdef CONFIG_FTRACE_MCOUNT_RECORD +#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY +#define MCOUNT_REC() . = ALIGN(8); \ + __start_mcount_loc = .; \ + KEEP(*(__patchable_function_entries)) \ + __stop_mcount_loc = .; +#else #define MCOUNT_REC() . = ALIGN(8); \ __start_mcount_loc = .; \ KEEP(*(__mcount_loc)) \ __stop_mcount_loc = .; +#endif #else #define MCOUNT_REC() #endif |