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The story begun when i`ve started to make indentation fixes in the DAC960 driver.
And in order to ensure i didn`t broke anything i was checking a diff between the
resulting object files.
Surprisingly enough i`ve realised soon that indeed some indentation changes
give gcc a reason to produce different code.
One of the cases is below, all three of them are in the attached .tar.gz file.
The code in question is the 2.5.72-bk1 kernel, however there was no changes
in the related code for some time, so plain .72 should be safe.
The examples are in the form of pairs of a C diff, and a "objdump -d" output diff.
The C diff:
diff -X scripts/Xrule -urN 25/drivers/block/DAC960.c 25dac/drivers/block/DAC960.c
--- 25/drivers/block/DAC960.c 2003-06-17 01:09:50.000000000 +0400
+++ 25dac/drivers/block/DAC960.c 2003-06-29 22:11:01.000000000 +0400
@@ -272,8 +272,7 @@
dma_addr_t RequestSenseDMA;
struct pci_pool *RequestSensePool = NULL;
- if (Controller->FirmwareType == DAC960_V1_Controller)
- {
+ if (Controller->FirmwareType == DAC960_V1_Controller) {
CommandAllocationLength = offsetof(DAC960_Command_T, V1.EndMarker);
CommandAllocationGroupSize = DAC960_V1_CommandAllocationGroupSize;
ScatterGatherPool = pci_pool_create("DAC960_V1_ScatterGather",
--- ./origDAC960.o.d 2003-06-29 21:02:55.000000000 +0400
+++ ./newDAC960.o.d 2003-06-29 22:13:46.000000000 +0400
@@ -1,5 +1,5 @@
-origDAC960.o: file format elf32-i386
+./newDAC960.o: file format elf32-i386
Disassembly of section .text:
@@ -5837,7 +5837,7 @@
52a8: 84 c0 test %al,%al
52aa: 75 14 jne 52c0 <DAC960_V1_ProcessCompletedCommand+0x80>
52ac: 0f 0b ud2a
- 52ae: 7d 0d jge 52bd <DAC960_V1_ProcessCompletedCommand+0x7d>
+ 52ae: 7c 0d jl 52bd <DAC960_V1_ProcessCompletedCommand+0x7d>
52b0: 27 daa
52b1: 00 00 add %al,(%eax)
52b3: 00 8d b6 00 00 00 add %cl,0xb6(%ebp)
@@ -5951,7 +5951,7 @@
5421: 84 c0 test %al,%al
5423: 0f 85 97 fe ff ff jne 52c0 <DAC960_V1_ProcessCompletedCommand+0x80>
5429: 0f 0b ud2a
- 542b: 8f 0d 27 00 00 00 popl 0x27
+ 542b: 8e 0d 27 00 00 00 movl 0x27,%cs
5431: e9 8a fe ff ff jmp 52c0 <DAC960_V1_ProcessCompletedCommand+0x80>
5436: 89 1c 24 mov %ebx,(%esp,1)
5439: e8 fc ff ff ff call 543a <DAC960_V1_ProcessCompletedCommand+0x1fa>
@@ -7414,7 +7414,7 @@
6ba2: 84 c0 test %al,%al
6ba4: 75 0a jne 6bb0 <DAC960_V2_ProcessCompletedCommand+0xa0>
6ba6: 0f 0b ud2a
- 6ba8: bc 11 27 00 00 mov $0x2711,%esp
+ 6ba8: bb 11 27 00 00 mov $0x2711,%ebx
6bad: 00 89 f6 83 bc 24 add %cl,0x24bc83f6(%ecx)
6bb3: 84 00 test %al,(%eax)
6bb5: 00 00 add %al,(%eax)
Thats it.
The point is i thought and hoped that gcc abstract syntax tree constructor is
indentation invariant, and that is seemingly not true.
regards, Samium Gromoff
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