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Date: Tue, 13 Oct 2015 13:28:50 +0200
From: Alex Dowad <>
Subject: [PATCHv3 1/3] fix matching errors for overwritten registers in x86 CFI generation script

thanks to R. Felker for noticing 2 separate problems:

- binary ops like ADD, AND, etc. overwrite the 2nd operand, not the 1st.
  this confusion resulted from mixing up Intel and GNU asm syntax.

- the regexps used to identify clobbered registers would erroneously match
  index registers. in other words, the following asm:

    mov $0, (%eax,%ebx,4)

...would cause EBX to be considered as overwritten, which might prevent a
debugger from displaying a variable's value in a higher stack frame.

Here is the latest iteration. I have merged 2 previously separate commits, and
fixed up the matching of registers (for the purpose of identifying overwritten

As usual, thanks for the feedback. AD

 tools/add-cfi.i386.awk | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/add-cfi.i386.awk b/tools/add-cfi.i386.awk
index 5dc8794..bd7932f 100644
--- a/tools/add-cfi.i386.awk
+++ b/tools/add-cfi.i386.awk
@@ -184,13 +184,13 @@ function trashed(register) {
 # this does NOT exhaustively check for all possible instructions which could
 # overwrite a register value inherited from the caller (just the common ones)
-/mov.*,%e(ax|bx|cx|dx|si|di|bp)/  { trashed(get_reg2()) }
-/(add|addl|sub|subl|and|or|xor|lea|sal|sar|shl|shr) %e(ax|bx|cx|dx|si|di|bp),/ {
-  trashed(get_reg1())
+/mov.*,%e(ax|bx|cx|dx|si|di|bp)$/  { trashed(get_reg2()) }
+/(add|addl|sub|subl|and|or|xor|lea|sal|sar|shl|shr).*,%e(ax|bx|cx|dx|si|di|bp)$/ {
+  trashed(get_reg2())
-/^i?mul [^,]*$/                    { trashed("eax"); trashed("edx") }
-/^i?mul %e(ax|bx|cx|dx|si|di|bp),/ { trashed(get_reg1()) }
-/^i?div/                           { trashed("eax"); trashed("edx") }
+/^i?mul [^,]*$/                      { trashed("eax"); trashed("edx") }
+/^i?mul.*,%e(ax|bx|cx|dx|si|di|bp)$/ { trashed(get_reg2()) }
+/^i?div/                             { trashed("eax"); trashed("edx") }
 /(dec|inc|not|neg|pop) %e(ax|bx|cx|dx|si|di|bp)/  { trashed(get_reg()) }
 /cpuid/ { trashed("eax"); trashed("ebx"); trashed("ecx"); trashed("edx") }

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