Le 19/06/2023 à 11:47, Naveen N Rao a écrit : > Commit 67361cf8071286 ("powerpc/ftrace: Handle large kernel configs") > added ftrace support for ppc64 kernel images with a text section larger > than 32MB. The patch did two things: > 1. Add stubs at the end of .text to branch into ftrace_[regs_]caller for > functions that were out of branch range. > 2. Re-purpose linker-generated long branches to _mcount to instead branch > to ftrace_[regs_]caller. > > Before that, we only supported kernel .text up to ~32MB. With the above, > we now support up to ~96MB: > - The first 32MB of kernel text can branch directly into > ftrace_[regs_]caller since that symbol is usually at the beginning. > - The modified long_branch from (2) above is used by the next 32MB of > kernel text. > - The next 32MB of kernel text can use the stub at the end of text to > branch back to ftrace_[regs_]caller. > > While re-purposing the long branch works in practice, it still restricts > ftrace to kernel text up to ~96MB. The stub at the end of kernel text > from (1) already enables us to extend ftrace support for kernel text > up to 64MB, which fulfils the original requirement. Further, once we > switch to -fpatchable-function-entry, there will not be a long branch > that we can use. > > Stop re-purposing the linker-generated long branches for ftrace to > simplify the code. If there are good reasons to support ftrace on > kernels beyond 64MB, we can consider adding support by using > -fpatchable-function-entry. > > Signed-off-by: Naveen N Rao <nav...@kernel.org>
Reviewed-by: Christophe Leroy <christophe.le...@csgroup.eu> > --- > arch/powerpc/kernel/trace/ftrace.c | 110 +++++------------------------ > 1 file changed, 17 insertions(+), 93 deletions(-) > > diff --git a/arch/powerpc/kernel/trace/ftrace.c > b/arch/powerpc/kernel/trace/ftrace.c > index ef4e49c2c37781..278bf8e52b6e89 100644 > --- a/arch/powerpc/kernel/trace/ftrace.c > +++ b/arch/powerpc/kernel/trace/ftrace.c > @@ -28,13 +28,7 @@ > #include <asm/syscall.h> > #include <asm/inst.h> > > -/* > - * We generally only have a single long_branch tramp and at most 2 or 3 plt > - * tramps generated. But, we don't use the plt tramps currently. We also > allot > - * 2 tramps after .text and .init.text. So, we only end up with around 3 > usable > - * tramps in total. Set aside 8 just to be sure. > - */ > -#define NUM_FTRACE_TRAMPS 8 > +#define NUM_FTRACE_TRAMPS 2 > static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS]; > > static ppc_inst_t > @@ -100,11 +94,6 @@ static int is_bl_op(ppc_inst_t op) > return (ppc_inst_val(op) & ~PPC_LI_MASK) == PPC_RAW_BL(0); > } > > -static int is_b_op(ppc_inst_t op) > -{ > - return (ppc_inst_val(op) & ~PPC_LI_MASK) == PPC_RAW_BRANCH(0); > -} > - > static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op) > { > int offset; > @@ -227,11 +216,7 @@ static unsigned long find_ftrace_tramp(unsigned long ip) > { > int i; > > - /* > - * We have the compiler generated long_branch tramps at the end > - * and we prefer those > - */ > - for (i = NUM_FTRACE_TRAMPS - 1; i >= 0; i--) > + for (i = 0; i < NUM_FTRACE_TRAMPS; i++) > if (!ftrace_tramps[i]) > continue; > else if (is_offset_in_branch_range(ftrace_tramps[i] - ip)) > @@ -240,75 +225,6 @@ static unsigned long find_ftrace_tramp(unsigned long ip) > return 0; > } > > -static int add_ftrace_tramp(unsigned long tramp) > -{ > - int i; > - > - for (i = 0; i < NUM_FTRACE_TRAMPS; i++) > - if (!ftrace_tramps[i]) { > - ftrace_tramps[i] = tramp; > - return 0; > - } > - > - return -1; > -} > - > -/* > - * If this is a compiler generated long_branch trampoline (essentially, a > - * trampoline that has a branch to _mcount()), we re-write the branch to > - * instead go to ftrace_[regs_]caller() and note down the location of this > - * trampoline. > - */ > -static int setup_mcount_compiler_tramp(unsigned long tramp) > -{ > - int i; > - ppc_inst_t op; > - unsigned long ptr; > - > - /* Is this a known long jump tramp? */ > - for (i = 0; i < NUM_FTRACE_TRAMPS; i++) > - if (ftrace_tramps[i] == tramp) > - return 0; > - > - /* New trampoline -- read where this goes */ > - if (copy_inst_from_kernel_nofault(&op, (void *)tramp)) { > - pr_debug("Fetching opcode failed.\n"); > - return -1; > - } > - > - /* Is this a 24 bit branch? */ > - if (!is_b_op(op)) { > - pr_debug("Trampoline is not a long branch tramp.\n"); > - return -1; > - } > - > - /* lets find where the pointer goes */ > - ptr = find_bl_target(tramp, op); > - > - if (ptr != ppc_global_function_entry((void *)_mcount)) { > - pr_debug("Trampoline target %p is not _mcount\n", (void *)ptr); > - return -1; > - } > - > - /* Let's re-write the tramp to go to ftrace_[regs_]caller */ > - if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS)) > - ptr = ppc_global_function_entry((void *)ftrace_regs_caller); > - else > - ptr = ppc_global_function_entry((void *)ftrace_caller); > - > - if (patch_branch((u32 *)tramp, ptr, 0)) { > - pr_debug("REL24 out of range!\n"); > - return -1; > - } > - > - if (add_ftrace_tramp(tramp)) { > - pr_debug("No tramp locations left\n"); > - return -1; > - } > - > - return 0; > -} > - > static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long > addr) > { > unsigned long tramp, ip = rec->ip; > @@ -331,13 +247,10 @@ static int __ftrace_make_nop_kernel(struct dyn_ftrace > *rec, unsigned long addr) > > pr_devel("ip:%lx jumps to %lx", ip, tramp); > > - if (setup_mcount_compiler_tramp(tramp)) { > - /* Are other trampolines reachable? */ > - if (!find_ftrace_tramp(ip)) { > - pr_err("No ftrace trampolines reachable from %ps\n", > - (void *)ip); > - return -EINVAL; > - } > + /* Are ftrace trampolines reachable? */ > + if (!find_ftrace_tramp(ip)) { > + pr_err("No ftrace trampolines reachable from %ps\n", (void > *)ip); > + return -EINVAL; > } > > if (patch_instruction((u32 *)ip, ppc_inst(PPC_RAW_NOP()))) { > @@ -725,6 +638,17 @@ void ftrace_free_init_tramp(void) > } > } > > +static void __init add_ftrace_tramp(unsigned long tramp) > +{ > + int i; > + > + for (i = 0; i < NUM_FTRACE_TRAMPS; i++) > + if (!ftrace_tramps[i]) { > + ftrace_tramps[i] = tramp; > + return; > + } > +} > + > int __init ftrace_dyn_arch_init(void) > { > unsigned int *tramp[] = { ftrace_tramp_text, ftrace_tramp_init };