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RISC-V: Prohibit relaxing the initial gp generation#9
Merged
palmer-dabbelt merged 1 commit intoriscv-nextfrom Mar 31, 2017
Merged
RISC-V: Prohibit relaxing the initial gp generation#9palmer-dabbelt merged 1 commit intoriscv-nextfrom
palmer-dabbelt merged 1 commit intoriscv-nextfrom
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I've added an additional linker relaxation that relaxes two instruction pc-relative sequences to one instruction gp relative sequences when possible. This sequence now optimizes the initial gp generation to mv gp, gp which is obviously bogus. The fix is to disable relaxations when setting up gp, preventing the linker from relaxing away this setup code.
aswaterman
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Mar 30, 2017
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Approved, assuming you and @kito-cheng come to agreement on the general strategy.
zongbox
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Sep 18, 2018
Wrapping the _start function with ENTRY and END to insert ENDBR32 at function entry when CET is enabled. Since _start now includes CFI, without "cfi_undefined (eip)", unwinder may not terminate at _start and we will get Program received signal SIGSEGV, Segmentation fault. 0xf7dc661e in ?? () from /lib/libgcc_s.so.1 Missing separate debuginfos, use: dnf debuginfo-install libgcc-8.2.1-3.0.fc28.i686 (gdb) bt #0 0xf7dc661e in ?? () from /lib/libgcc_s.so.1 riscvarchive#1 0xf7dc7c18 in _Unwind_Backtrace () from /lib/libgcc_s.so.1 riscvarchive#2 0xf7f0d809 in __GI___backtrace (array=array@entry=0xffffc7d0, size=size@entry=20) at ../sysdeps/i386/backtrace.c:127 riscvarchive#3 0x08049254 in compare (p1=p1@entry=0xffffcad0, p2=p2@entry=0xffffcad4) at backtrace-tst.c:12 riscvarchive#4 0xf7e2a28c in msort_with_tmp (p=p@entry=0xffffca5c, b=b@entry=0xffffcad0, n=n@entry=2) at msort.c:65 riscvarchive#5 0xf7e29f64 in msort_with_tmp (n=2, b=0xffffcad0, p=0xffffca5c) at msort.c:53 riscvarchive#6 msort_with_tmp (p=p@entry=0xffffca5c, b=b@entry=0xffffcad0, n=n@entry=5) at msort.c:53 riscvarchive#7 0xf7e29f64 in msort_with_tmp (n=5, b=0xffffcad0, p=0xffffca5c) at msort.c:53 riscvarchive#8 msort_with_tmp (p=p@entry=0xffffca5c, b=b@entry=0xffffcad0, n=n@entry=10) at msort.c:53 riscvarchive#9 0xf7e29f64 in msort_with_tmp (n=10, b=0xffffcad0, p=0xffffca5c) at msort.c:53 riscvarchive#10 msort_with_tmp (p=p@entry=0xffffca5c, b=b@entry=0xffffcad0, n=n@entry=20) at msort.c:53 riscvarchive#11 0xf7e2a5b6 in msort_with_tmp (n=20, b=0xffffcad0, p=0xffffca5c) at msort.c:297 riscvarchive#12 __GI___qsort_r (b=b@entry=0xffffcad0, n=n@entry=20, s=s@entry=4, cmp=cmp@entry=0x8049230 <compare>, arg=arg@entry=0x0) at msort.c:297 riscvarchive#13 0xf7e2a84d in __GI_qsort (b=b@entry=0xffffcad0, n=n@entry=20, s=s@entry=4, cmp=cmp@entry=0x8049230 <compare>) at msort.c:308 riscvarchive#14 0x080490f6 in main (argc=2, argv=0xffffcbd4) at backtrace-tst.c:39 FAIL: debug/backtrace-tst [BZ #23606] * sysdeps/i386/start.S: Include <sysdep.h> (_start): Use ENTRY/END to insert ENDBR32 at entry when CET is enabled. Add cfi_undefined (eip). Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
palmer-dabbelt
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Mar 18, 2019
Commit 27761a1 ("Refactor atfork handlers") introduced a lock, atfork_lock, around fork handler list accesses. It turns out that this lock occasionally results in self-deadlocks in malloc/tst-mallocfork2: (gdb) bt #0 __lll_lock_wait_private () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:63 #1 0x00007f160c6f927a in __run_fork_handlers (who=(unknown: 209394016), who@entry=atfork_run_prepare) at register-atfork.c:116 #2 0x00007f160c6b7897 in __libc_fork () at ../sysdeps/nptl/fork.c:58 #3 0x00000000004027d6 in sigusr1_handler (signo=<optimized out>) at tst-mallocfork2.c:80 #4 sigusr1_handler (signo=<optimized out>) at tst-mallocfork2.c:64 #5 <signal handler called> #6 0x00007f160c6f92e4 in __run_fork_handlers (who=who@entry=atfork_run_parent) at register-atfork.c:136 #7 0x00007f160c6b79a2 in __libc_fork () at ../sysdeps/nptl/fork.c:152 #8 0x0000000000402567 in do_test () at tst-mallocfork2.c:156 #9 0x0000000000402dd2 in support_test_main (argc=1, argv=0x7ffc81ef1ab0, config=config@entry=0x7ffc81ef1970) at support_test_main.c:350 #10 0x0000000000402362 in main (argc=<optimized out>, argv=<optimized out>) at ../support/test-driver.c:168 If no locking happens in the single-threaded case (where fork is expected to be async-signal-safe), this deadlock is avoided. (pthread_atfork is not required to be async-signal-safe, so a fork call from a signal handler interrupting pthread_atfork is not a problem.)
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I've added an additional linker relaxation that relaxes two instruction
pc-relative sequences to one instruction gp relative sequences when
possible. This sequence now optimizes the initial gp generation to
mv gp, gp
which is obviously bogus. The fix is to disable relaxations when
setting up gp, preventing the linker from relaxing away this setup code.