| Denys Vlasenko | 33a9f34 | 2022-01-23 15:46:05 +0100 | [diff] [blame] | 1 | /* Add SORT_BY_ALIGNMENT to linker script (found in busybox_unstripped.out): |
| 2 | ## .rodata : { *(.rodata SORT_BY_ALIGNMENT(.rodata.*) .gnu.linkonce.r.*) } |
| 3 | ## .data : { *(.data SORT_BY_ALIGNMENT(.data.*) .gnu.linkonce.d.*) } |
| 4 | ## .bss : { *(.bss SORT_BY_ALIGNMENT(.bss.*) .gnu.linkonce.b.*) } |
| 5 | ## This will eliminate most of the padding (~3kb). |
| 6 | ## Hmm, "ld --sort-section alignment" should do it too. |
| 7 | ## |
| 8 | ## There is a ld hack which is meant to decrease disk usage |
| 9 | ## at the cost of more RAM usage (??!!) in standard ld script: |
| 10 | ## . = ALIGN (0x1000) - ((0x1000 - .) & (0x1000 - 1)); . = DATA_SEGMENT_ALIGN (0x1000, 0x1000); |
| 11 | ## Replace it with: |
| 12 | ## . = ALIGN (0x1000); . = DATA_SEGMENT_ALIGN (0x1000, 0x1000); |
| 13 | ## to unconditionally align .data to the next page boundary, |
| 14 | ## instead of "next page, plus current offset in this page" |
| 15 | */ |
| 16 | |
| 17 | /* To reduce the number of VMAs each bbox process has, |
| 18 | ## move *(.bss SORT_BY_ALIGNMENT(.bss.*) ...) |
| 19 | ## part from .bss : {...} block to .data : { ... } block. |
| 20 | ## (This usually increases .data section by only one page). |
| 21 | ## Result: |
| 22 | ## |
| 23 | ## text data bss dec hex filename |
| 24 | ## 1050792 560 7580 1058932 102874 busybox.bss |
| 25 | ## 1050792 8149 0 1058941 10287d busybox.nobss |
| 26 | ## |
| 27 | ## $ exec busybox.bss pmap $$ |
| 28 | ## 0000000008048000 1028K r-xp /path/to/busybox.bss |
| 29 | ## 0000000008149000 8K rw-p /path/to/busybox.bss |
| 30 | ## 000000000814b000 4K rw-p [ anon ] <---- this VMA is eliminated |
| 31 | ## 00000000085f5000 4K ---p [heap] |
| 32 | ## 00000000085f6000 4K rw-p [heap] |
| 33 | ## 00000000f7778000 8K rw-p [ anon ] |
| 34 | ## 00000000f777a000 12K r--p [vvar] |
| 35 | ## 00000000f777d000 8K r-xp [vdso] |
| 36 | ## 00000000ff7e9000 132K rw-p [stack] |
| 37 | ## |
| 38 | ## $ exec busybox.nobss pmap $$ |
| 39 | ## 0000000008048000 1028K r-xp /path/to/busybox.nobss |
| 40 | ## 0000000008149000 12K rw-p /path/to/busybox.nobss |
| 41 | ## 00000000086f0000 4K ---p [heap] |
| 42 | ## 00000000086f1000 4K rw-p [heap] |
| 43 | ## 00000000f7783000 8K rw-p [ anon ] |
| 44 | ## 00000000f7785000 12K r--p [vvar] |
| 45 | ## 00000000f7788000 8K r-xp [vdso] |
| 46 | ## 00000000ffac0000 132K rw-p [stack] |
| 47 | */ |