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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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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> |
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| .. | ||
| syscalls | ||
| .gitignore | ||
| alternative.c | ||
| asm-offsets.c | ||
| audit.c | ||
| cache.c | ||
| compat_audit.c | ||
| drivers.c | ||
| entry.S | ||
| firmware.c | ||
| ftrace.c | ||
| hardware.c | ||
| head.S | ||
| hpmc.S | ||
| inventory.c | ||
| irq.c | ||
| jump_label.c | ||
| kgdb.c | ||
| kprobes.c | ||
| Makefile | ||
| module.c | ||
| module.lds | ||
| pa7300lc.c | ||
| pacache.S | ||
| parisc_ksyms.c | ||
| patch.c | ||
| pci-dma.c | ||
| pci.c | ||
| pdc_chassis.c | ||
| pdc_cons.c | ||
| pdt.c | ||
| perf_asm.S | ||
| perf_images.h | ||
| perf.c | ||
| process.c | ||
| processor.c | ||
| ptrace.c | ||
| real2.S | ||
| setup.c | ||
| signal32.c | ||
| signal32.h | ||
| signal.c | ||
| smp.c | ||
| stacktrace.c | ||
| sys_parisc32.c | ||
| sys_parisc.c | ||
| syscall.S | ||
| time.c | ||
| topology.c | ||
| traps.c | ||
| unaligned.c | ||
| unwind.c | ||
| vmlinux.lds.S | ||