diff options
| author | Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> | 2018-10-17 01:55:00 +0530 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2018-10-20 13:26:47 +1100 |
| commit | 67361cf80712867329a9cd3ff0e3171545cfc867 (patch) | |
| tree | 1946e36e656030e2dbd947f0190dcd3e56e748f5 /arch/powerpc/kernel/vmlinux.lds.S | |
| parent | dd0e144a632bcf2b5a6f04e2628e32b16d499277 (diff) | |
powerpc/ftrace: Handle large kernel configs
Currently, we expect to be able to reach ftrace_caller() from all
ftrace-enabled functions through a single relative branch. With large
kernel configs, we see functions outside of 32MB of ftrace_caller()
causing ftrace_init() to bail.
In such configurations, gcc/ld emits two types of trampolines for mcount():
1. A long_branch, which has a single branch to mcount() for functions that
are one hop away from mcount():
c0000000019e8544 <00031b56.long_branch._mcount>:
c0000000019e8544: 4a 69 3f ac b c00000000007c4f0 <._mcount>
2. A plt_branch, for functions that are farther away from mcount():
c0000000051f33f8 <0008ba04.plt_branch._mcount>:
c0000000051f33f8: 3d 82 ff a4 addis r12,r2,-92
c0000000051f33fc: e9 8c 04 20 ld r12,1056(r12)
c0000000051f3400: 7d 89 03 a6 mtctr r12
c0000000051f3404: 4e 80 04 20 bctr
We can reuse those trampolines for ftrace if we can have those
trampolines go to ftrace_caller() instead. However, with ABIv2, we
cannot depend on r2 being valid. As such, we use only the long_branch
trampolines by patching those to instead branch to ftrace_caller or
ftrace_regs_caller.
In addition, we add additional trampolines around .text and .init.text
to catch locations that are covered by the plt branches. This allows
ftrace to work with most large kernel configurations.
For now, we always patch the trampolines to go to ftrace_regs_caller,
which is slightly inefficient. This can be optimized further at a later
point.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/vmlinux.lds.S')
| -rw-r--r-- | arch/powerpc/kernel/vmlinux.lds.S | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index ac0ceb31b336..2d50b362f835 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -102,6 +102,9 @@ SECTIONS #endif /* careful! __ftr_alt_* sections need to be close to .text */ *(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text); +#ifdef CONFIG_PPC64 + *(.tramp.ftrace.text); +#endif SCHED_TEXT CPUIDLE_TEXT LOCK_TEXT @@ -184,7 +187,15 @@ SECTIONS */ . = ALIGN(STRICT_ALIGN_SIZE); __init_begin = .; - INIT_TEXT_SECTION(PAGE_SIZE) :kernel + . = ALIGN(PAGE_SIZE); + .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) { + _sinittext = .; + INIT_TEXT + _einittext = .; +#ifdef CONFIG_PPC64 + *(.tramp.ftrace.init); +#endif + } :kernel /* .exit.text is discarded at runtime, not link time, * to deal with references from __bug_table |