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carbon throwing objc exceptions
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carbon throwing objc exceptions

  • Subject: carbon throwing objc exceptions
  • From: Joel Reymont <email@hidden>
  • Date: Fri, 11 Sep 2009 22:40:34 +0100
I'm looking at CFStringRefToUTF8 [1] , a function in the Firefox source code. This function, like many others is bracketed in NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT
and NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT, i.e.

@try {
...
} @catch(NSException *_exn) {
nsObjCExceptionLog(_exn);
}
return NS_ERROR_FAILURE;

[1] http://mxr.mozilla.org/mozilla-central/source/xpcom/io/nsLocalFileOSX.mm#2225

It looks harmless but the assembler dump is horrendous (below). 2/3 or 3/4 of
this function (more?) are taken by the exception setup and cleanup. ObjC
exceptions are zero-cost on x86-64 but very expensive on x86-32.

I think this is ham-handed use of ObjC exceptions but I'm told that this is done this way because Carbon can throw ObjC exceptions. Can someone confirm this, please, or suggest a less evil way of handling ObjC exceptions arising from Carbon?

	Thanks, Joel

---

Breakpoint 1, CFStringReftoUTF8 (aInStrRef=0x2614fc0, aOutStr=@0xbfffec58) at
../../../mozilla-central/xpcom/io/nsLocalFileOSX.mm:2187
2187 NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
(gdb) disas
Dump of assembler code for function CFStringRefToUTF8:
0x00bf8ff0 <CFStringRefToUTF8+0>: push ëp
0x00bf8ff1 <CFStringRefToUTF8+1>: mov %esp,ëp
0x00bf8ff3 <CFStringRefToUTF8+3>: push %esi
0x00bf8ff4 <CFStringRefToUTF8+4>: push ëx
0x00bf8ff5 <CFStringRefToUTF8+5>: sub $0xb0,%esp
0x00bf8ffb <CFStringRefToUTF8+11>: call 0xbf9000 <CFStringRefToUTF8+16>
0x00bf9000 <CFStringRefToUTF8+16>: pop ëx
0x00bf9001 <CFStringRefToUTF8+17>: mov êx,-0x6c(ëp)
0x00bf9004 <CFStringRefToUTF8+20>: mov íx,-0x70(ëp)
0x00bf9007 <CFStringRefToUTF8+23>: lea -0x64(ëp),%esia
0x00bf900a <CFStringRefToUTF8+26>: mov %esi,(%esp)
0x00bf900d <CFStringRefToUTF8+29>: call 0xd1b0f4
<dyld_stub_objc_exception_try_enter>
0x00bf9012 <CFStringRefToUTF8+34>: mov %esi,(%esp)
0x00bf9015 <CFStringRefToUTF8+37>: call 0xd1aecc <dyld_stub__setjmp>
0x00bf901a <CFStringRefToUTF8+42>: test êx,êx
0x00bf901c <CFStringRefToUTF8+44>: je 0xbf9080 <CFStringRefToUTF8+144>
0x00bf901e <CFStringRefToUTF8+46>: lea -0x64(ëp),%esi
0x00bf9021 <CFStringRefToUTF8+49>: mov %esi,(%esp)
0x00bf9024 <CFStringRefToUTF8+52>: call 0xd1b0e2
<dyld_stub_objc_exception_extract>
0x00bf9029 <CFStringRefToUTF8+57>: mov êx,-0x74(ëp)
0x00bf902c <CFStringRefToUTF8+60>: mov %esi,(%esp)
0x00bf902f <CFStringRefToUTF8+63>: call 0xd1b0f4
<dyld_stub_objc_exception_try_enter>
0x00bf9034 <CFStringRefToUTF8+68>: mov %esi,(%esp)
0x00bf9037 <CFStringRefToUTF8+71>: call 0xd1aecc <dyld_stub__setjmp>
0x00bf903c <CFStringRefToUTF8+76>: test êx,êx
0x00bf903e <CFStringRefToUTF8+78>: je 0xbf9110 <CFStringRefToUTF8+288>
0x00bf9044 <CFStringRefToUTF8+84>: lea -0x64(ëp),êx
0x00bf9047 <CFStringRefToUTF8+87>: mov êx,(%esp)
0x00bf904a <CFStringRefToUTF8+90>: call 0xd1b0e2
<dyld_stub_objc_exception_extract>
0x00bf904f <CFStringRefToUTF8+95>: mov êx,-0x74(ëp)
0x00bf9052 <CFStringRefToUTF8+98>: mov -0x74(ëp),íx
0x00bf9055 <CFStringRefToUTF8+101>: test íx,íx
0x00bf9057 <CFStringRefToUTF8+103>: jne 0xbf920a <CFStringRefToUTF8+538>
0x00bf905d <CFStringRefToUTF8+109>: lea -0x64(ëp),êx
0x00bf9060 <CFStringRefToUTF8+112>: mov êx,(%esp)
0x00bf9063 <CFStringRefToUTF8+115>: call 0xd1b0fa
<dyld_stub_objc_exception_try_exit>
0x00bf9068 <CFStringRefToUTF8+120>: mov $0x80004005,ëx
0x00bf906d <CFStringRefToUTF8+125>: mov ëx,êx
0x00bf906f <CFStringRefToUTF8+127>: add $0xb0,%esp
0x00bf9075 <CFStringRefToUTF8+133>: pop ëx
0x00bf9076 <CFStringRefToUTF8+134>: pop %esi
0x00bf9077 <CFStringRefToUTF8+135>: leave
0x00bf9078 <CFStringRefToUTF8+136>: ret
0x00bf9079 <CFStringRefToUTF8+137>: nopl 0x0(êx)
0x00bf9080 <CFStringRefToUTF8+144>: mov -0x6c(ëp),êx
0x00bf9083 <CFStringRefToUTF8+147>: mov êx,(%esp)
0x00bf9086 <CFStringRefToUTF8+150>: call 0xd19336
<dyld_stub_CFStringGetLength>
0x00bf908b <CFStringRefToUTF8+155>: mov êx,%esi
0x00bf908d <CFStringRefToUTF8+157>: mov êx,-0x84(ëp)
0x00bf9093 <CFStringRefToUTF8+163>: movl $0x0,-0x88(ëp)
0x00bf909d <CFStringRefToUTF8+173>: mov -0x6c(ëp),ìx
0x00bf90a0 <CFStringRefToUTF8+176>: lea -0xc(ëp),êx
0x00bf90a3 <CFStringRefToUTF8+179>: mov êx,0x20(%esp)
0x00bf90a7 <CFStringRefToUTF8+183>: movl $0x0,0x1c(%esp)
0x00bf90af <CFStringRefToUTF8+191>: movl $0x0,0x18(%esp)
0x00bf90b7 <CFStringRefToUTF8+199>: movl $0x0,0x14(%esp)
0x00bf90bf <CFStringRefToUTF8+207>: movl $0x0,0x10(%esp)
0x00bf90c7 <CFStringRefToUTF8+215>: movl $0x8000100,0xc(%esp)
0x00bf90cf <CFStringRefToUTF8+223>: mov -0x88(ëp),êx
0x00bf90d5 <CFStringRefToUTF8+229>: mov -0x84(ëp),íx
0x00bf90db <CFStringRefToUTF8+235>: mov êx,0x4(%esp)
0x00bf90df <CFStringRefToUTF8+239>: mov íx,0x8(%esp)
0x00bf90e3 <CFStringRefToUTF8+243>: mov ìx,(%esp)
0x00bf90e6 <CFStringRefToUTF8+246>: call 0xd19318
<dyld_stub_CFStringGetBytes>
0x00bf90eb <CFStringRefToUTF8+251>: mov $0x80004005,ëx
0x00bf90f0 <CFStringRefToUTF8+256>: cmp êx,%esi
0x00bf90f2 <CFStringRefToUTF8+258>: je 0xbf9180 <CFStringRefToUTF8+400>
0x00bf90f8 <CFStringRefToUTF8+264>: lea -0x64(ëp),êx
0x00bf90fb <CFStringRefToUTF8+267>: mov êx,(%esp)
0x00bf90fe <CFStringRefToUTF8+270>: call 0xd1b0fa
<dyld_stub_objc_exception_try_exit>
0x00bf9103 <CFStringRefToUTF8+275>: mov ëx,êx
0x00bf9105 <CFStringRefToUTF8+277>: add $0xb0,%esp
0x00bf910b <CFStringRefToUTF8+283>: pop ëx
0x00bf910c <CFStringRefToUTF8+284>: pop %esi
0x00bf910d <CFStringRefToUTF8+285>: leave
0x00bf910e <CFStringRefToUTF8+286>: ret
0x00bf910f <CFStringRefToUTF8+287>: nop
0x00bf9110 <CFStringRefToUTF8+288>: mov -0x74(ëp),êx
0x00bf9113 <CFStringRefToUTF8+291>: mov êx,0x4(%esp)
0x00bf9117 <CFStringRefToUTF8+295>: mov 0x38b944(ëx),êx
0x00bf911d <CFStringRefToUTF8+301>: mov êx,(%esp)
0x00bf9120 <CFStringRefToUTF8+304>: call 0xd1b0e8
<dyld_stub_objc_exception_match>
0x00bf9125 <CFStringRefToUTF8+309>: test êx,êx
0x00bf9127 <CFStringRefToUTF8+311>: je 0xbf9170 <CFStringRefToUTF8+384>
0x00bf9129 <nsObjCExceptionLog+0>: mov 0x38b008(ëx),êx
0x00bf912f <nsObjCExceptionLog+6>: mov êx,0x4(%esp)
0x00bf9133 <nsObjCExceptionLog+10>: mov -0x74(ëp),íx
0x00bf9136 <nsObjCExceptionLog+13>: mov íx,(%esp)
0x00bf9139 <nsObjCExceptionLog+16>: call 0xd1b100 <dyld_stub_objc_msgSend>
0x00bf913e <nsObjCExceptionLog+21>: mov êx,%esi
0x00bf9140 <nsObjCExceptionLog+23>: mov 0x38b00c(ëx),êx
0x00bf9146 <nsObjCExceptionLog+29>: mov êx,0x4(%esp)
0x00bf914a <nsObjCExceptionLog+33>: mov -0x74(ëp),ìx
0x00bf914d <nsObjCExceptionLog+36>: mov ìx,(%esp)
0x00bf9150 <nsObjCExceptionLog+39>: call 0xd1b100 <dyld_stub_objc_msgSend>
0x00bf9155 <nsObjCExceptionLog+44>: mov %esi,0x8(%esp)
0x00bf9159 <nsObjCExceptionLog+48>: mov êx,0x4(%esp)
0x00bf915d <nsObjCExceptionLog+52>: lea 0x36ad48(ëx),êx
0x00bf9163 <nsObjCExceptionLog+58>: mov êx,(%esp)
0x00bf9166 <nsObjCExceptionLog+61>: call 0xd1a0ce <dyld_stub_NSLog>
0x00bf916b <nsObjCExceptionLog+66>: jmp 0xbf905d <CFStringRefToUTF8+109>
0x00bf9170 <CFStringRefToUTF8+384>: lea -0x64(ëp),êx
0x00bf9173 <CFStringRefToUTF8+387>: mov êx,(%esp)
0x00bf9176 <CFStringRefToUTF8+390>: call 0xd1b0fa
<dyld_stub_objc_exception_try_exit>
0x00bf917b <CFStringRefToUTF8+395>: jmp 0xbf9052 <CFStringRefToUTF8+98>
0x00bf9180 <CFStringRefToUTF8+400>: mov -0x70(ëp),êx
0x00bf9183 <CFStringRefToUTF8+403>: mov -0xc(ëp),íx
0x00bf9186 <CFStringRefToUTF8+406>: call 0xc34010
<_ZN19nsACString_internal9SetLengthEj>
0x00bf918b <CFStringRefToUTF8+411>: mov -0x70(ëp),êx
0x00bf918e <CFStringRefToUTF8+414>: mov 0x4(êx),êx
0x00bf9191 <CFStringRefToUTF8+417>: mov $0x8007000e,ëx
0x00bf9196 <CFStringRefToUTF8+422>: cmp -0xc(ëp),êx
0x00bf9199 <CFStringRefToUTF8+425>: jne 0xbf90f8 <CFStringRefToUTF8+264>
0x00bf919f <CFStringRefToUTF8+431>: mov -0x70(ëp),ëx
0x00bf91a2 <_ZN19nsACString_internal12BeginWritingEv+0>: mov
$0xffffffff,íx
0x00bf91a7 <_ZN19nsACString_internal12BeginWritingEv+5>: mov ëx,êx
0x00bf91a9 <_ZN19nsACString_internal12BeginWritingEv+7>: call 0xc35490
<_ZN19nsACString_internal13EnsureMutableEj>
0x00bf91ae <_ZN19nsACString_internal12BeginWritingEv+12>: xor ìx,ìx
0x00bf91b0 <_ZN19nsACString_internal12BeginWritingEv+14>: test êx,êx
0x00bf91b2 <_ZN19nsACString_internal12BeginWritingEv+16>: je 0xbf91b6
<CFStringRefToUTF8+454>
0x00bf91b4 <_ZN19nsACString_internal12BeginWritingEv+18>: mov (ëx),ìx
0x00bf91b6 <CFStringRefToUTF8+454>: mov %esi,-0x7c(ëp)
0x00bf91b9 <CFStringRefToUTF8+457>: movl $0x0,-0x80(ëp)
0x00bf91c0 <CFStringRefToUTF8+464>: mov -0x6c(ëp),êx
0x00bf91c3 <CFStringRefToUTF8+467>: lea -0xc(ëp),íx
0x00bf91c6 <CFStringRefToUTF8+470>: mov íx,0x20(%esp)
0x00bf91ca <CFStringRefToUTF8+474>: mov -0xc(ëp),íx
0x00bf91cd <CFStringRefToUTF8+477>: mov íx,0x1c(%esp)
0x00bf91d1 <CFStringRefToUTF8+481>: mov ìx,0x18(%esp)
0x00bf91d5 <CFStringRefToUTF8+485>: movl $0x0,0x14(%esp)
0x00bf91dd <CFStringRefToUTF8+493>: movl $0x0,0x10(%esp)
0x00bf91e5 <CFStringRefToUTF8+501>: movl $0x8000100,0xc(%esp)
0x00bf91ed <CFStringRefToUTF8+509>: mov -0x80(ëp),íx
0x00bf91f0 <CFStringRefToUTF8+512>: mov -0x7c(ëp),ìx
0x00bf91f3 <CFStringRefToUTF8+515>: mov íx,0x4(%esp)
0x00bf91f7 <CFStringRefToUTF8+519>: mov ìx,0x8(%esp)
0x00bf91fb <CFStringRefToUTF8+523>: mov êx,(%esp)
0x00bf91fe <CFStringRefToUTF8+526>: call 0xd19318
<dyld_stub_CFStringGetBytes>
0x00bf9203 <CFStringRefToUTF8+531>: xor ëx,ëx
0x00bf9205 <CFStringRefToUTF8+533>: jmp 0xbf90f8 <CFStringRefToUTF8+264>
0x00bf920a <CFStringRefToUTF8+538>: mov -0x74(ëp),ìx
0x00bf920d <CFStringRefToUTF8+541>: mov ìx,(%esp)
0x00bf9210 <CFStringRefToUTF8+544>: call 0xd1b0ee
<dyld_stub_objc_exception_throw>
End of assembler dump.

---
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