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authorSergio Durigan Junior <sergiodj@redhat.com>2013-04-22 09:20:33 +0000
committerSergio Durigan Junior <sergiodj@redhat.com>2013-04-22 09:20:33 +0000
commit9991b20795a23272b07dd2214aa3ee0196b61f0b (patch)
tree3af720925d6ca84704b5f68f894994f1d0889ae5 /gdb/go-lang.h
parentbfeb4a285ab62875ca5dafedc0c51d06493a1952 (diff)
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Andrew Haley found a bug on GDB running on ARM when using
--enable-64-bit-bfd. Basically the issue happens when dealing with "bl" instructions: GDB does branch destination calculation and (wrongly) sign-extends the PC. Here is a piece of his original message explaining the problem: > next_pc = arm_get_next_pc (frame, get_frame_pc (frame)); > > /* The Linux kernel offers some user-mode helpers in a high page. We can > not read this page (as of 2.6.23), and even if we could then we couldn't > set breakpoints in it, and even if we could then the atomic operations > would fail when interrupted. They are all called as functions and return > to the address in LR, so step to there instead. */ > if (next_pc > 0xffff0000) > next_pc = get_frame_register_unsigned (frame, ARM_LR_REGNUM); > > arm_insert_single_step_breakpoint (gdbarch, aspace, next_pc); > > Unfortunately, branch destination addresses are SIGN EXTENDED to 64 > bits. So, > > (top-gdb) p/x next_pc > $14 = 0xffffffffb6df2864 > > Which triggers the next_pc = get_frame_register_unsigned(), and we > cannot step into any branches because the destination PC is wrong. Anyway, the fix is simple and Andrew himself provided it for us. It took a while for me to figure out how to trigger the bug (in order to write a testcase for it), but I finally made it. The attached patch fixes the problem (by casting to `unsigned long' instead of just `long'), and also includes a testcase to reproduce the issue. gdb/ChangeLog: 2013-04-22 Andrew Haley <aph@redhat.com> * arm-tdep.c (BranchDest): Cast result as "unsigned long", instead of "long". gdb/testsuite/ChangeLog: 2013-04-22 Sergio Durigan Junior <sergiodj@redhat.com> * gdb.arch/arm-bl-branch-dest.c: New file. * gdb.arch/arm-bl-branch-dest.exp: Likewise.
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