path: root/sys/amd64
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authorBruce Evans <bde@FreeBSD.org>2018-06-02 04:25:09 +0000
committerBruce Evans <bde@FreeBSD.org>2018-06-02 04:25:09 +0000
commitdbe3061729e3b1b0a56370d529b4a3f90543a0c3 (patch)
tree664b2d8c8cad4e0ee5e8f1e7352d8c580f8b4149 /sys/amd64
parent0059e7102ff4b95a43406f94c0de8b3b6f2a6aa9 (diff)
Fix recent breakages of kernel profiling, mostly on i386 (high resolution
kernel profiling remains broken). memmove() was broken using ALTENTRY(). ALTENTRY() is only different from ENTRY() in the profiling case, and its use in that case was sort of backwards. The backwardness magically turned memmove() into memcpy() instead of completely breaking it. Only the high resolution parts of profiling itself were broken. Use ordinary ENTRY() for memmove(). Turn bcopy() into a tail call to memmove() to reduce complications. This gives slightly different pessimizations and profiling lossage. The pessimizations are minimized by not using a frame pointer() for bcopy(). Calls to profiling functions from exception trampolines were not relocated. This caused crashes on the first exception. Fix this using function pointers. Addresses of exception handlers in trampolines were not relocated. This caused unknown offsets in the profiling data. Relocate by abusing setidt_disp as for pmc although this is slower than necessary and requires namespace pollution. pmc seems to be missing some relocations. Stack traces and lots of other things in debuggers need similar relocations. Most user addresses were misclassified as unknown kernel addresses and then ignored. Treat all unknown addresses as user. Now only user addresses in the kernel text range are significantly misclassified (as known kernel addresses). The ibrs functions didn't preserve enough registers. This is the only recent breakage on amd64. Although these functions are written in asm, in the profiling case they call profiling functions which are mostly for the C ABI, so they only have to save call-used registers. They also have to save arg and return registers in some cases and actually save them in all cases to reduce complications. They end up saving all registers except %ecx on i386 and %r10 and %r11 on amd64. Saving these is only needed for 1 caller on each of amd64 and i386. Save them there. This is slightly simpler. Remove saving %ecx in handle_ibrs_exit on i386. Both handle_ibrs_entry and handle_ibrs_exit use %ecx, but only the latter needed to or did save it. But saving it there doesn't work for the profiling case. amd64 has more automatic saving of the most common scratch registers %rax, %rcx and %rdx (its complications for %r10 are from unusual use of %r10 by SYSCALL). Thus profiling of handle_ibrs_exit_rs() was not broken, and I didn't simplify the saving by moving the saving of these registers from it to the caller.
Notes: svn path=/head/; revision=334520
Diffstat (limited to 'sys/amd64')
1 files changed, 8 insertions, 1 deletions
diff --git a/sys/amd64/amd64/exception.S b/sys/amd64/amd64/exception.S
index 08948c0904e0..c49547d8fa66 100644
--- a/sys/amd64/amd64/exception.S
+++ b/sys/amd64/amd64/exception.S
@@ -463,8 +463,16 @@ fast_syscall_common:
movq PCPU(SCRATCH_RSP),%r11 /* %r11 already saved */
movq %r11,TF_RSP(%rsp) /* user stack pointer */
+ /*
+ * Save a few arg registers early to free them for use in
+ * handle_ibrs_entry(). %r10 is especially tricky. It is not an
+ * arg register, but it holds the arg register %rcx. Profiling
+ * preserves %rcx, but may clobber %r10. Profiling may also
+ * clobber %r11, but %r11 (original %eflags) has been saved.
+ */
movq %rax,TF_RAX(%rsp) /* syscall number */
movq %rdx,TF_RDX(%rsp) /* arg 3 */
+ movq %r10,TF_RCX(%rsp) /* arg 4 */
call handle_ibrs_entry
movq PCPU(CURPCB),%r11
@@ -475,7 +483,6 @@ fast_syscall_common:
movq $2,TF_ERR(%rsp)
movq %rdi,TF_RDI(%rsp) /* arg 1 */
movq %rsi,TF_RSI(%rsp) /* arg 2 */
- movq %r10,TF_RCX(%rsp) /* arg 4 */
movq %r8,TF_R8(%rsp) /* arg 5 */
movq %r9,TF_R9(%rsp) /* arg 6 */
movq %rbx,TF_RBX(%rsp) /* C preserved */