[binutils-gdb] gas: scfi: bugfixes for SCFI state propagation

[Indu Bhagat <ibhagat@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f1c5d46cae3fa4a3c41c05c796c69d52eef97067

commit f1c5d46cae3fa4a3c41c05c796c69d52eef97067
Author: Indu Bhagat <indu.bhagat@oracle.com>
Date:   Wed Apr 10 13:46:37 2024 -0700

    gas: scfi: bugfixes for SCFI state propagation
    
    There are two state propagation functions in SCFI machinery - forward
    and backward flow.  The patch addresses two issues:
      - In forward_flow_scfi_state (), the state being compared in forward flow
        must be that at the exit of a prev bb and that at the entry of the
        next bb.  The variable holding the state to be compared was
        previously (erroneously) stale.
      - In cmp_scfi_state (), the assumption that two different control
        flows, leading to the same basic block, cannot have a mismatched
        notion of CFA base register, is not true.  Remove the assertion and
        instead return err if mismatch.
    
    Fixing these issues helps correctly synthesize CFI, when previously
    SCFI was erroring out for an otherwise valid input asm.
    
    gas/
            * scfi.c (cmp_scfi_state): Remove assertion and return mismatch
            in return value as applicable.
            (forward_flow_scfi_state): Update state object to be the same as
            the exit state of the prev bb before comparing.
    
    gas/testsuite/
            * gas/scfi/x86_64/scfi-x86-64.exp: Add new test.
            * gas/scfi/x86_64/scfi-cfg-5.d: New test.
            * gas/scfi/x86_64/scfi-cfg-5.l: New test.
            * gas/scfi/x86_64/scfi-cfg-5.s: New test.

Diff:
---
 gas/scfi.c                                    | 20 ++++++++------
 gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.d    | 39 +++++++++++++++++++++++++++
 gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.l    |  2 ++
 gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.s    | 32 ++++++++++++++++++++++
 gas/testsuite/gas/scfi/x86_64/scfi-x86-64.exp |  2 ++
 5 files changed, 87 insertions(+), 8 deletions(-)

diff --git a/gas/scfi.c b/gas/scfi.c
index 37cc85cfed7..929ea8a73e1 100644
--- a/gas/scfi.c
+++ b/gas/scfi.c
@@ -155,7 +155,7 @@ cmp_scfi_state (scfi_stateS *state1, scfi_stateS *state2)
   int ret;
 
   if (!state1 || !state2)
-    ret = 1;
+    return 1;
 
   /* Skip comparing the scratch[] value of registers.  The user visible
      unwind information is derived from the regs[] from the SCFI state.  */
@@ -164,10 +164,12 @@ cmp_scfi_state (scfi_stateS *state1, scfi_stateS *state2)
 
   /* For user functions which perform dynamic stack allocation, after switching
      t REG_FP based CFA tracking, it is perfectly possible to have stack usage
-     in some control flows.  However, double-checking that all control flows
-     have the same idea of CFA tracking before this wont hurt.  */
-  gas_assert (state1->regs[REG_CFA].base == state2->regs[REG_CFA].base);
-  if (state1->regs[REG_CFA].base == REG_SP)
+     in some control flows.  Further, the different control flows may even not
+     have the same idea of CFA tracking (likely later necessitating generation
+     of .cfi_remember_state / .cfi_restore_state pair).  */
+  ret |= state1->regs[REG_CFA].base != state2->regs[REG_CFA].base;
+
+  if (!ret && state1->regs[REG_CFA].base == REG_SP)
     ret |= state1->stack_size != state2->stack_size;
 
   ret |= state1->traceable_p != state2->traceable_p;
@@ -911,11 +913,11 @@ gen_scfi_ops (ginsnS *ginsn, scfi_stateS *state)
   return ret;
 }
 
-/* Recursively perform forward flow of the (unwind information) SCFI state
+/* Recursively perform forward flow of the (unwind information) SCFI STATE
    starting at basic block GBB.
 
-   The forward flow process propagates the SCFI state at exit of a basic block
-   to the successor basic block.
+   The core of forward flow process takes the SCFI state at the entry of a bb
+   and updates it incrementally as per the semantics of each ginsn in the bb.
 
    Returns error code, if any.  */
 
@@ -961,6 +963,8 @@ forward_flow_scfi_state (gcfgS *gcfg, gbbS *gbb, scfi_stateS *state)
       bb_for_each_edge(gbb, gedge)
 	{
 	  gbb = gedge->dst_bb;
+	  /* Ensure that the state is the one from the exit of the prev bb.  */
+	  memcpy (state, prev_bb->exit_state, sizeof (scfi_stateS));
 	  if (gbb->visited)
 	    {
 	      ret = cmp_scfi_state (gbb->entry_state, state);
diff --git a/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.d b/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.d
new file mode 100644
index 00000000000..5a0a2e1f927
--- /dev/null
+++ b/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.d
@@ -0,0 +1,39 @@
+#as: --scfi=experimental -W
+#as:
+#objdump: -Wf
+#name: Synthesize CFI in presence of control flow 5
+#...
+Contents of the .eh_frame section:
+
+00000000 0+0014 0+0000 CIE
+  Version:               1
+  Augmentation:          "zR"
+  Code alignment factor: 1
+  Data alignment factor: -8
+  Return address column: 16
+  Augmentation data:     1b
+  DW_CFA_def_cfa: r7 \(rsp\) ofs 8
+  DW_CFA_offset: r16 \(rip\) at cfa-8
+  DW_CFA_nop
+  DW_CFA_nop
+
+0+0018 0+002c 0000001c FDE cie=00000000 pc=0+0000..0+0017
+  DW_CFA_advance_loc: 1 to 0+0001
+  DW_CFA_def_cfa_offset: 16
+  DW_CFA_offset: r6 \(rbp\) at cfa-16
+  DW_CFA_advance_loc: 3 to 0+0004
+  DW_CFA_def_cfa_register: r6 \(rbp\)
+  DW_CFA_advance_loc: 5 to 0+0009
+  DW_CFA_remember_state
+  DW_CFA_advance_loc: 6 to 0+000f
+  DW_CFA_def_cfa_register: r7 \(rsp\)
+  DW_CFA_restore: r6 \(rbp\)
+  DW_CFA_def_cfa_offset: 8
+  DW_CFA_advance_loc: 1 to 0+0010
+  DW_CFA_restore_state
+  DW_CFA_advance_loc: 6 to 0+0016
+  DW_CFA_def_cfa_register: r7 \(rsp\)
+  DW_CFA_restore: r6 \(rbp\)
+  DW_CFA_def_cfa_offset: 8
+
+#pass
diff --git a/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.l b/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.l
new file mode 100644
index 00000000000..abca835a642
--- /dev/null
+++ b/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.l
@@ -0,0 +1,2 @@
+.*Assembler messages:
+.*5: Warning: SCFI ignores most user-specified CFI directives
diff --git a/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.s b/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.s
new file mode 100644
index 00000000000..80b081ffe07
--- /dev/null
+++ b/gas/testsuite/gas/scfi/x86_64/scfi-cfg-5.s
@@ -0,0 +1,32 @@
+	.text
+	.globl foo
+	.type foo, @function
+foo:
+	.cfi_startproc
+	push  %rbp
+	.cfi_def_cfa_offset 16
+	.cfi_offset %rbp, -16
+	mov   %rsp, %rbp
+	.cfi_def_cfa_register %rbp
+	cmpl  $-1, %eax
+	jne .L1
+.L2:
+	.cfi_remember_state
+	call bar
+	pop  %rbp
+	.cfi_def_cfa_register %rsp
+	.cfi_restore %rbp
+	.cfi_def_cfa_offset 8
+	ret
+
+.L1:
+	.cfi_restore_state
+	testq %rax, %rax
+	je .L2
+	pop %rbp
+	.cfi_def_cfa_register %rsp
+	.cfi_restore %rbp
+	.cfi_def_cfa_offset 8
+	ret
+	.cfi_endproc
+	.size foo,.-foo
diff --git a/gas/testsuite/gas/scfi/x86_64/scfi-x86-64.exp b/gas/testsuite/gas/scfi/x86_64/scfi-x86-64.exp
index 63f0d7e4700..a91dc9df9e5 100644
--- a/gas/testsuite/gas/scfi/x86_64/scfi-x86-64.exp
+++ b/gas/testsuite/gas/scfi/x86_64/scfi-x86-64.exp
@@ -82,6 +82,8 @@ if  { ([istarget "x86_64-*-*"] && ![istarget "x86_64-*-linux*-gnux32"]) } then {
     run_list_test "scfi-cfg-3" "--scfi=experimental --warn"
     run_dump_test "scfi-cfg-4"
     run_list_test "scfi-cfg-4" "--scfi=experimental --warn"
+    run_dump_test "scfi-cfg-5"
+    run_list_test "scfi-cfg-5" "--scfi=experimental --warn"
     run_dump_test "scfi-asm-marker-1"
     run_list_test "scfi-asm-marker-1" "--scfi=experimental --warn"
     run_dump_test "scfi-asm-marker-2"