in reply to Re^3: (OT) How can I do unless(caller) { main; } in C using GCC in Windows?
in thread (OT) How can I do unless(caller) { main; } in C using GCC in Windows?

Thanks for your help! I'm able to create the .o objects and objdump their contents, but I don't know how to look in the dumps to find entry points.

C:\> gcc -c scriptedmain.c scriptedmain.h
C:\> gcc -c test.c scriptedmain.c scriptedmain.h
C:\> objdump -x scriptedmain.o
scriptedmain.o:     file format pe-i386
scriptedmain.o
architecture: i386, flags 0x00000039:
HAS_RELOC, HAS_DEBUG, HAS_SYMS, HAS_LOCALS
start address 0x00000000

Characteristics 0x104
    line numbers stripped
    32 bit words

Time/Date        Wed Dec 31 19:00:00 1969
Magic            0000
MajorLinkerVersion    0
MinorLinkerVersion    0
SizeOfCode        00000000
SizeOfInitializedData    00000000
SizeOfUninitializedData    00000000
AddressOfEntryPoint    00000000
BaseOfCode        00000000
BaseOfData        00000000
ImageBase        00000000
SectionAlignment    00000000
FileAlignment        00000000
MajorOSystemVersion    0
MinorOSystemVersion    0
MajorImageVersion    0
MinorImageVersion    0
MajorSubsystemVersion    0
MinorSubsystemVersion    0
Win32Version        00000000
SizeOfImage        00000000
SizeOfHeaders        00000000
CheckSum        00000000
Subsystem        00000000    (unspecified)
DllCharacteristics    00000000
SizeOfStackReserve    00000000
SizeOfStackCommit    00000000
SizeOfHeapReserve    00000000
SizeOfHeapCommit    00000000
LoaderFlags        00000000
NumberOfRvaAndSizes    00000000

The Data Directory
Entry 0 00000000 00000000 Export Directory [.edata (or where ever we f
+ound it)]
Entry 1 00000000 00000000 Import Directory [parts of .idata]
Entry 2 00000000 00000000 Resource Directory [.rsrc]
Entry 3 00000000 00000000 Exception Directory [.pdata]
Entry 4 00000000 00000000 Security Directory
Entry 5 00000000 00000000 Base Relocation Directory [.reloc]
Entry 6 00000000 00000000 Debug Directory
Entry 7 00000000 00000000 Description Directory
Entry 8 00000000 00000000 Special Directory
Entry 9 00000000 00000000 Thread Storage Directory [.tls]
Entry a 00000000 00000000 Load Configuration Directory
Entry b 00000000 00000000 Bound Import Directory
Entry c 00000000 00000000 Import Address Table Directory
Entry d 00000000 00000000 Delay Import Directory
Entry e 00000000 00000000 CLR Runtime Header
Entry f 00000000 00000000 Reserved

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000034  00000000  00000000  000000b4  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .data         00000000  00000000  00000000  00000000  2**2
                  ALLOC, LOAD, DATA
  2 .bss          00000000  00000000  00000000  00000000  2**2
                  ALLOC
  3 .rdata        00000024  00000000  00000000  000000e8  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
SYMBOL TABLE:
[  0](sec -2)(fl 0x00)(ty   0)(scl 103) (nx 1) 0x00000000 scriptedmain
+.c
File 
[  2](sec  1)(fl 0x00)(ty  20)(scl   2) (nx 1) 0x00000000 _meaning_of_
+life
AUX tagndx 0 ttlsiz 0x0 lnnos 0 next 0
[  4](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x34 nreloc 3 nlnno 0
[  6](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .data
AUX scnlen 0x0 nreloc 0 nlnno 0
[  8](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .bss
AUX scnlen 0x0 nreloc 0 nlnno 0
[ 10](sec  4)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rdata
AUX scnlen 0x21 nreloc 0 nlnno 0
[ 12](sec  1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000a .weak._main.
+_meaning_of_life
[ 13](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 ___main
[ 14](sec  0)(fl 0x00)(ty  20)(scl 105) (nx 1) 0x00000000 _main
AUX lnno 1 size 0x0 tagndx 12
[ 16](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _printf


RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
00000014 DISP32            ___main
00000024 dir32             .rdata
00000029 DISP32            _printf

C:\> objdump -x test.o
test.o:     file format pe-i386
test.o
architecture: i386, flags 0x00000039:
HAS_RELOC, HAS_DEBUG, HAS_SYMS, HAS_LOCALS
start address 0x00000000

Characteristics 0x104
    line numbers stripped
    32 bit words

Time/Date        Wed Dec 31 19:00:00 1969
Magic            0000
MajorLinkerVersion    0
MinorLinkerVersion    0
SizeOfCode        00000000
SizeOfInitializedData    00000000
SizeOfUninitializedData    00000000
AddressOfEntryPoint    00000000
BaseOfCode        00000000
BaseOfData        00000000
ImageBase        00000000
SectionAlignment    00000000
FileAlignment        00000000
MajorOSystemVersion    0
MinorOSystemVersion    0
MajorImageVersion    0
MinorImageVersion    0
MajorSubsystemVersion    0
MinorSubsystemVersion    0
Win32Version        00000000
SizeOfImage        00000000
SizeOfHeaders        00000000
CheckSum        00000000
Subsystem        00000000    (unspecified)
DllCharacteristics    00000000
SizeOfStackReserve    00000000
SizeOfStackCommit    00000000
SizeOfHeapReserve    00000000
SizeOfHeapCommit    00000000
LoaderFlags        00000000
NumberOfRvaAndSizes    00000000

The Data Directory
Entry 0 00000000 00000000 Export Directory [.edata (or where ever we f
+ound it)]
Entry 1 00000000 00000000 Import Directory [parts of .idata]
Entry 2 00000000 00000000 Resource Directory [.rsrc]
Entry 3 00000000 00000000 Exception Directory [.pdata]
Entry 4 00000000 00000000 Security Directory
Entry 5 00000000 00000000 Base Relocation Directory [.reloc]
Entry 6 00000000 00000000 Debug Directory
Entry 7 00000000 00000000 Description Directory
Entry 8 00000000 00000000 Special Directory
Entry 9 00000000 00000000 Thread Storage Directory [.tls]
Entry a 00000000 00000000 Load Configuration Directory
Entry b 00000000 00000000 Bound Import Directory
Entry c 00000000 00000000 Import Address Table Directory
Entry d 00000000 00000000 Delay Import Directory
Entry e 00000000 00000000 CLR Runtime Header
Entry f 00000000 00000000 Reserved

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         0000002c  00000000  00000000  000000b4  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .data         00000000  00000000  00000000  00000000  2**2
                  ALLOC, LOAD, DATA
  2 .bss          00000000  00000000  00000000  00000000  2**2
                  ALLOC
  3 .rdata        00000024  00000000  00000000  000000e0  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
SYMBOL TABLE:
[  0](sec -2)(fl 0x00)(ty   0)(scl 103) (nx 1) 0x00000000 test.c
File 
[  2](sec  1)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _main
[  3](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x2a nreloc 4 nlnno 0
[  5](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .data
AUX scnlen 0x0 nreloc 0 nlnno 0
[  7](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .bss
AUX scnlen 0x0 nreloc 0 nlnno 0
[  9](sec  4)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rdata
AUX scnlen 0x21 nreloc 0 nlnno 0
[ 11](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 1) 0x00000000 ___main
AUX tagndx 0 ttlsiz 0x0 lnnos 0 next 0
[ 13](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _meaning_of_
+life
[ 14](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _printf


RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
0000000a DISP32            ___main
0000000f DISP32            _meaning_of_life
0000001a dir32             .rdata
0000001f DISP32            _printf

[download]

If I'm reading these correctly, both seem to contain the entry points _main and __main. At least the offsets differ, but compiling scriptedmain by referring to the entry point offset doesn't work.

C:\Users\andrew\Desktop\src\scriptedmain\c>gcc -o scriptedmain -e00000
+014 scriptedmain.c scriptedmain.h
c:/strawberry/c/bin/../lib/gcc/i686-w64-mingw32/4.4.3/../../../../i686
+-w64-mingw32/lib/libmingw32.a(lib32_libmingw32_a-crt0_c.o): In functi
+on `main':
/opt/W64_156151-src.32/build-crt/../mingw-w64-crt/crt/crt0_c.c:18: und
+efined reference to `WinMain@16'
collect2: ld returned 1 exit status

[download]

Replies are listed 'Best First'.
Re^5: (OT) How can I do unless(caller) { main; } in C using GCC in Windows?
by Anonymous Monk on Sep 12, 2012 at 23:40 UTC

    Ok, so whatever that is, its a bug in libmingw32

    Report bugs to mingw folks :)

    I tried 

    gcc -o scriptedmain scriptedmain.c  -s -Wl,-subsystem,console  -nostdl
+ib

    [download]

    Which avoid libmingw32 but this fails with 

    undefined reference to `___main'
undefined reference to `_printf'
undefined reference to `_printf'

    [download]

    Naturally -e ___main doesn't help anything 

    $ gcc -o scriptedmain scriptedmain.c  -s -Wl,-subsystem,console  -nost
+dlib -e ___main
c:/mingw/bin/../lib/gcc/mingw32/4.7.0/../../../../mingw32/bin/ld.exe: 
+warning: cannot find entry symbol ___main; defaul
ing to 00401000

    [download]

    So however you're supposed to work it, ask the mingw folks

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