diff options
Diffstat (limited to 'arch/s390/kernel/ftrace.c')
| -rw-r--r-- | arch/s390/kernel/ftrace.c | 57 |
1 files changed, 40 insertions, 17 deletions
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c index f908e42e11c4..fcb009d3edde 100644 --- a/arch/s390/kernel/ftrace.c +++ b/arch/s390/kernel/ftrace.c @@ -1,7 +1,7 @@ /* * Dynamic function tracer architecture backend. * - * Copyright IBM Corp. 2009 + * Copyright IBM Corp. 2009,2014 * * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>, * Martin Schwidefsky <schwidefsky@de.ibm.com> @@ -17,6 +17,7 @@ #include <asm/asm-offsets.h> #include "entry.h" +void mcount_replace_code(void); void ftrace_disable_code(void); void ftrace_enable_insn(void); @@ -24,38 +25,50 @@ void ftrace_enable_insn(void); /* * The 64-bit mcount code looks like this: * stg %r14,8(%r15) # offset 0 - * > larl %r1,<&counter> # offset 6 - * > brasl %r14,_mcount # offset 12 + * larl %r1,<&counter> # offset 6 + * brasl %r14,_mcount # offset 12 * lg %r14,8(%r15) # offset 18 - * Total length is 24 bytes. The middle two instructions of the mcount - * block get overwritten by ftrace_make_nop / ftrace_make_call. + * Total length is 24 bytes. The complete mcount block initially gets replaced + * by ftrace_make_nop. Subsequent calls to ftrace_make_call / ftrace_make_nop + * only patch the jg/lg instruction within the block. + * Note: we do not patch the first instruction to an unconditional branch, + * since that would break kprobes/jprobes. It is easier to leave the larl + * instruction in and only modify the second instruction. * The 64-bit enabled ftrace code block looks like this: - * stg %r14,8(%r15) # offset 0 + * larl %r0,.+24 # offset 0 * > lg %r1,__LC_FTRACE_FUNC # offset 6 - * > lgr %r0,%r0 # offset 12 - * > basr %r14,%r1 # offset 16 - * lg %r14,8(%15) # offset 18 - * The return points of the mcount/ftrace function have the same offset 18. - * The 64-bit disable ftrace code block looks like this: - * stg %r14,8(%r15) # offset 0 + * br %r1 # offset 12 + * brcl 0,0 # offset 14 + * brc 0,0 # offset 20 + * The ftrace function gets called with a non-standard C function call ABI + * where r0 contains the return address. It is also expected that the called + * function only clobbers r0 and r1, but restores r2-r15. + * The return point of the ftrace function has offset 24, so execution + * continues behind the mcount block. + * larl %r0,.+24 # offset 0 * > jg .+18 # offset 6 - * > lgr %r0,%r0 # offset 12 - * > basr %r14,%r1 # offset 16 - * lg %r14,8(%15) # offset 18 + * br %r1 # offset 12 + * brcl 0,0 # offset 14 + * brc 0,0 # offset 20 * The jg instruction branches to offset 24 to skip as many instructions * as possible. */ asm( " .align 4\n" + "mcount_replace_code:\n" + " larl %r0,0f\n" "ftrace_disable_code:\n" " jg 0f\n" - " lgr %r0,%r0\n" - " basr %r14,%r1\n" + " br %r1\n" + " brcl 0,0\n" + " brc 0,0\n" "0:\n" " .align 4\n" "ftrace_enable_insn:\n" " lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n"); +#define MCOUNT_BLOCK_SIZE 24 +#define MCOUNT_INSN_OFFSET 6 #define FTRACE_INSN_SIZE 6 #else /* CONFIG_64BIT */ @@ -116,6 +129,16 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { +#ifdef CONFIG_64BIT + /* Initial replacement of the whole mcount block */ + if (addr == MCOUNT_ADDR) { + if (probe_kernel_write((void *) rec->ip - MCOUNT_INSN_OFFSET, + mcount_replace_code, + MCOUNT_BLOCK_SIZE)) + return -EPERM; + return 0; + } +#endif if (probe_kernel_write((void *) rec->ip, ftrace_disable_code, MCOUNT_INSN_SIZE)) return -EPERM; |