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Re: [ppc patch] shrink grubof build

From: Hollis Blanchard
Subject: Re: [ppc patch] shrink grubof build
Date: Tue, 14 Sep 2004 09:47:56 -0500

On Sep 14, 2004, at 9:00 AM, Hollis Blanchard wrote:

On Sep 14, 2004, at 6:17 AM, Stefan Reinauer wrote:

* Hollis Blanchard <address@hidden> [040914 02:59]:
This patch shrinks the size of the 'grubof' binary from >300K to ~60K

2004-09-13      Hollis Blanchard        <address@hidden>

        * conf/powerpc-ieee1275.rmk (grubof_LDFLAGS): add -N and -S

I see that -S makes sense (stripping debugger symbols), but -N (setting
text sections to writable) I don't fully understand...

That's what Marco and I said as well. :) However, that flag is used in the i386 build, and shrinks the PPC binary significantly as well.

grubof: 351219 bytes
grubof -S: 166131 bytes; objcopy -O binary: 146224 bytes
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x010000 0x00200000 0x00200000 0x13d68 0x13d68 R E 0x10000 LOAD 0x023d68 0x00223d68 0x00223d68 0x001b0 0x08bd4 RW 0x10000
grubof -S -N: 100723 bytes; objcopy -O binary: 81688 bytes
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
  LOAD           0x000080 0x00200000 0x00200000 0x13f18 0x1c93c RWE 0x10

I'm noticing the offset changed significantly, while obviously the in-memory size didn't. The ppc ABI (32- and 64-bit) say "Virtual addresses and file offsets for the 64-bit PowerPC processor family segments are congruent modulo 64 Kbytes (0x10000) or larger powers of 2." Apparently -N means "ignore the ABI" here, which is fine for us.

(Aside: Old World Open Firmware won't read a filesystem on a partition (only on a whole volume like a floppy disk), so OF can't load an ELF for me. To work around that I have a dumb stage1 (from the quik bootloader) that loads a blocklist into memory. So I objcopy -O binary and record that blocklist.)

I still can't fully explain why there is such a drastic difference in the binary output size (rather than the ELF size).


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