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[Bug ld/30145] No way to specify PE IMAGE_SCN_* characteristics
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From: |
pali at kernel dot org |
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Subject: |
[Bug ld/30145] No way to specify PE IMAGE_SCN_* characteristics |
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Date: |
Sat, 15 Apr 2023 10:40:19 +0000 |
https://sourceware.org/bugzilla/show_bug.cgi?id=30145
--- Comment #3 from Pali Rohár <pali at kernel dot org> ---
Ok, I have tested objcopy --set-section-flags on PE executable. Seems that it
is doing something, but only for some of the flags and I really do not
understand what it is doing. For me it looks like that objcopy
--set-section-flags sets random IMAGE_SCN_* characteristics...
Here is my test case and output from readpe after setting every flag via
objcopy --set-section-flags on simple PE executable with custom section
my_sect:
$ cat test-section-flags.c
__attribute__((section("my_sect"))) int val = 10;
int my_entry(void) { return val; }
$ x86_64-w64-mingw32-gcc -Wall -Wextra -nostartfiles -nodefaultlibs -nostdlib
-e my_entry test-section-flags.c -o test-section-flags.exe
$ readpe test-section-flags.exe 2>/dev/null | grep -A 11 my_sect
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000040
Characteristic Names
IMAGE_SCN_CNT_INITIALIZED_DATA
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
$ for flag in alloc load noload readonly debug code data rom exclude share
contents merge strings; do echo "Flags: $flag"; x86_64-w64-mingw32-objcopy
--set-section-flags my_sect=$flag test-section-flags.exe
test-section-flags-new.exe && readpe test-section-flags-new.exe 2>/dev/null |
grep -A 12 my_sect; echo; done
Flags: alloc
Name: my_sect
Virtual Size: 0x200 (512 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0 (0 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000080
Characteristic Names
IMAGE_SCN_CNT_UNINITIALIZED_DATA
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Flags: load
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000000
Characteristic Names
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Virtual Size: 0x20 (32 bytes)
Flags: noload
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc2000000
Characteristic Names
IMAGE_SCN_MEM_DISCARDABLE
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Flags: readonly
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0x40000000
Characteristic Names
IMAGE_SCN_MEM_READ
Section
Name: .rdata
Virtual Size: 0x20 (32 bytes)
Virtual Address: 0x3000
Flags: debug
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc2000040
Characteristic Names
IMAGE_SCN_CNT_INITIALIZED_DATA
IMAGE_SCN_MEM_DISCARDABLE
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Flags: code
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xe0000020
Characteristic Names
IMAGE_SCN_CNT_CODE
IMAGE_SCN_MEM_EXECUTE
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Flags: data
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000040
Characteristic Names
IMAGE_SCN_CNT_INITIALIZED_DATA
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Flags: rom
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000000
Characteristic Names
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Virtual Size: 0x20 (32 bytes)
Flags: exclude
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc2000000
Characteristic Names
IMAGE_SCN_MEM_DISCARDABLE
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Flags: share
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xd0000000
Characteristic Names
IMAGE_SCN_MEM_SHARED
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Flags: contents
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000000
Characteristic Names
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Virtual Size: 0x20 (32 bytes)
Flags: merge
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000000
Characteristic Names
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Virtual Size: 0x20 (32 bytes)
Flags: strings
Name: my_sect
Virtual Size: 0x4 (4 bytes)
Virtual Address: 0x2000
Size Of Raw Data: 0x200 (512 bytes)
Pointer To Raw Data: 0x600
Number Of Relocations: 0
Characteristics: 0xc0000000
Characteristic Names
IMAGE_SCN_MEM_READ
IMAGE_SCN_MEM_WRITE
Section
Name: .rdata
Virtual Size: 0x20 (32 bytes)
This --set-section-flags objcopy option should be properly documented for every
flag, what it is doing with PE executable, because from above output I'm really
not sure.
Now I remember that in past I was trying to set IMAGE_SCN_MEM_DISCARDABLE via
objcopy 2.31.1 and none of flags was able to do it (neither noload). But with
objcopy 2.39 it is possible via noload flag.
So... this --set-section-flags option looks like a good starting point for
setting section flags. Just it needs documentation and fixing/extending it for
other PE IMAGE_SCN_* flags.
And important is also ability to set or clear just one particular flag, because
currently --set-section-flags can just replace all existing flags by a new
flags specified in the command line option.
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