33a9f34df
Denys Vlasenko
2022-01-23
Subject
add busybox_ldscript.README.txt
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busybox_ldscript.README.txt+47 -0
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| + | /* Add SORT_BY_ALIGNMENT to linker script (found in busybox_unstripped.out): |
| + | ## .rodata : { *(.rodata SORT_BY_ALIGNMENT(.rodata.*) .gnu.linkonce.r.*) } |
| + | ## .data : { *(.data SORT_BY_ALIGNMENT(.data.*) .gnu.linkonce.d.*) } |
| + | ## .bss : { *(.bss SORT_BY_ALIGNMENT(.bss.*) .gnu.linkonce.b.*) } |
| + | ## This will eliminate most of the padding (~3kb). |
| + | ## Hmm, "ld --sort-section alignment" should do it too. |
| + | ## |
| + | ## There is a ld hack which is meant to decrease disk usage |
| + | ## at the cost of more RAM usage (??!!) in standard ld script: |
| + | ## . = ALIGN (0x1000) - ((0x1000 - .) & (0x1000 - 1)); . = DATA_SEGMENT_ALIGN (0x1000, 0x1000); |
| + | ## Replace it with: |
| + | ## . = ALIGN (0x1000); . = DATA_SEGMENT_ALIGN (0x1000, 0x1000); |
| + | ## to unconditionally align .data to the next page boundary, |
| + | ## instead of "next page, plus current offset in this page" |
| + | */ |
| + | |
| + | /* To reduce the number of VMAs each bbox process has, |
| + | ## move *(.bss SORT_BY_ALIGNMENT(.bss.*) ...) |
| + | ## part from .bss : {...} block to .data : { ... } block. |
| + | ## (This usually increases .data section by only one page). |
| + | ## Result: |
| + | ## |
| + | ## text data bss dec hex filename |
| + | ## 1050792 560 7580 1058932 102874 busybox.bss |
| + | ## 1050792 8149 0 1058941 10287d busybox.nobss |
| + | ## |
| + | ## $ exec busybox.bss pmap $$ |
| + | ## 0000000008048000 1028K r-xp /path/to/busybox.bss |
| + | ## 0000000008149000 8K rw-p /path/to/busybox.bss |
| + | ## 000000000814b000 4K rw-p [ anon ] <---- this VMA is eliminated |
| + | ## 00000000085f5000 4K ---p [heap] |
| + | ## 00000000085f6000 4K rw-p [heap] |
| + | ## 00000000f7778000 8K rw-p [ anon ] |
| + | ## 00000000f777a000 12K r--p [vvar] |
| + | ## 00000000f777d000 8K r-xp [vdso] |
| + | ## 00000000ff7e9000 132K rw-p [stack] |
| + | ## |
| + | ## $ exec busybox.nobss pmap $$ |
| + | ## 0000000008048000 1028K r-xp /path/to/busybox.nobss |
| + | ## 0000000008149000 12K rw-p /path/to/busybox.nobss |
| + | ## 00000000086f0000 4K ---p [heap] |
| + | ## 00000000086f1000 4K rw-p [heap] |
| + | ## 00000000f7783000 8K rw-p [ anon ] |
| + | ## 00000000f7785000 12K r--p [vvar] |
| + | ## 00000000f7788000 8K r-xp [vdso] |
| + | ## 00000000ffac0000 132K rw-p [stack] |
| + | */ |