Stop APE bare metal loader from reading beyond program image end (#574)

This allows e.g. `qemu-system-x86_64 -s o/examples/hello.com
-serial stdio` to work without having to add extra padding to
the end of the `hello.com` "disk image".

(The sector count computation is divided among two instructions
in the assembly code.  This is done on purpose, to prevent an
ASCII 0x27 (single quote) byte from appearing in the bare
metal loader code, which will break the shell script loader.
There is probably a better way.)

Co-authored-by: tkchia <tkchia-cosmo@gmx.com>
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tkchia 2022-09-04 15:19:08 +08:00 committed by GitHub
parent 9c017c98d3
commit 8569704c1d
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2 changed files with 5 additions and 0 deletions

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@ -563,6 +563,9 @@ SHSTUB2(ape_loader_dd_count,
HIDDEN(v_ape_realsectors =
MIN(0x70000 - IMAGE_BASE_REAL,
ROUNDUP(RVA(_edata), 4096)) / 512);
HIDDEN(v_ape_realslacksectors =
v_ape_realsectors - MIN(0x70000 - IMAGE_BASE_REAL,
ROUNDUP(RVA(_edata), 512)) / 512);
HIDDEN(v_ape_realpages = v_ape_realsectors / (4096 / 512));
HIDDEN(v_ape_highsectors =
(ROUNDUP(RVA(_edata), 512) / 512) - v_ape_realsectors);