From 6ca6366220ed285e29ee22f4cf5c68a0397cb005 Mon Sep 17 00:00:00 2001 From: Sven Schnelle Date: Wed, 5 Jun 2019 22:32:22 +0200 Subject: 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 : 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
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 : 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 Signed-off-by: Helge Deller --- arch/parisc/Kconfig | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/parisc/Kconfig') diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig index 4860efa91d7b..42875ff15671 100644 --- a/arch/parisc/Kconfig +++ b/arch/parisc/Kconfig @@ -59,6 +59,8 @@ config PARISC select HAVE_ARCH_KGDB select HAVE_KPROBES select HAVE_KRETPROBES + select HAVE_DYNAMIC_FTRACE if $(cc-option,-fpatchable-function-entry=1,1) + select HAVE_FTRACE_MCOUNT_RECORD if HAVE_DYNAMIC_FTRACE help The PA-RISC microprocessor is designed by Hewlett-Packard and used -- cgit v1.2.3