From 685de8c2990a04fba5e2954b7ff089a2c641071f Mon Sep 17 00:00:00 2001 From: Sergio Durigan Junior Date: Sat, 25 Nov 2017 01:13:03 -0500 Subject: [PATCH] Fix PR gdb/22491: Regression when setting SystemTap probe semaphores Pedro has kindly pointed out that gdb.arch/amd64-stap-optional-prefix.exp was failing after my C++-ification patches touching the probe interface. The failure is kind of cryptic: 77 break -pstap bar 78 Breakpoint 3 at 0x40048d 79 (gdb) PASS: gdb.arch/amd64-stap-optional-prefix.exp: bar: break -pstap bar 80 continue 81 Continuing. 82 83 Program received signal SIGILL, Illegal instruction. 84 main () at amd64-stap-optional-prefix.S:26 85 26 STAP_PROBE1(probe, foo, (%rsp)) It took me a while to figure out where this SIGILL is coming from. Initially I thought it was something related to writing registers to the inferior when dealing with probe arguments, but I discarded this since the arguments were not touching any registers. In the end, this was a mistake that was introduced during the review process of the patch. When setting/clearing a SystemTap probe's semaphore, the code was using 'm_address' (which refers the probe's address) instead of 'm_sem_addr' (which refers to the semaphore's address). This caused GDB to write a bogus value in the wrong memory position, which in turn caused the SIGILL. I am pushing this patch to correct the mistake. On a side note: I told Pedro that the BuildBot hadn't caught the failure during my try build, and for a moment there was a suspicion that the BuildBot might be at fault here. However, I investigate this and noticed that I only did one try build, with a patch that was correctly using 'm_sem_addr' where applicable, and therefore no failure should have happened indeed. I probably should have requested another try build after addressing the review's comments, but they were mostly basic and I didn't think it was needed. Oh, well. 2017-11-25 Sergio Durigan Junior PR gdb/22491 * stap-probe.c (relocate_address): New function. (stap_probe::get_relocated_address): Use 'relocate_address'. (stap_probe::set_semaphore): Use 'relocate_address' and pass 'm_sem_addr'. (stap_probe::clear_semaphore): Likewise. --- gdb/stap-probe.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c index 63100c9fb3c..9f4e00845a4 100644 --- a/gdb/stap-probe.c +++ b/gdb/stap-probe.c @@ -1278,13 +1278,21 @@ stap_probe::parse_arguments (struct gdbarch *gdbarch) } } +/* Helper function to relocate an address. */ + +static CORE_ADDR +relocate_address (CORE_ADDR address, struct objfile *objfile) +{ + return address + ANOFFSET (objfile->section_offsets, + SECT_OFF_DATA (objfile)); +} + /* Implementation of the get_relocated_address method. */ CORE_ADDR stap_probe::get_relocated_address (struct objfile *objfile) { - return this->get_address () + ANOFFSET (objfile->section_offsets, - SECT_OFF_DATA (objfile)); + return relocate_address (this->get_address (), objfile); } /* Given PROBE, returns the number of arguments present in that probe's @@ -1455,7 +1463,7 @@ stap_modify_semaphore (CORE_ADDR address, int set, struct gdbarch *gdbarch) void stap_probe::set_semaphore (struct objfile *objfile, struct gdbarch *gdbarch) { - stap_modify_semaphore (this->get_relocated_address (objfile), 1, gdbarch); + stap_modify_semaphore (relocate_address (m_sem_addr, objfile), 1, gdbarch); } /* Implementation of the 'clear_semaphore' method. */ @@ -1463,7 +1471,7 @@ stap_probe::set_semaphore (struct objfile *objfile, struct gdbarch *gdbarch) void stap_probe::clear_semaphore (struct objfile *objfile, struct gdbarch *gdbarch) { - stap_modify_semaphore (this->get_relocated_address (objfile), 0, gdbarch); + stap_modify_semaphore (relocate_address (m_sem_addr, objfile), 0, gdbarch); } /* Implementation of the 'get_static_ops' method. */ -- 2.30.2