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The improvements are:
- use most of the default "Makefile" for standard packaging;
- also use the default ".gitignore" with for the derived assets;
- don't impose so many $CFLAGS on the user. GCC still needs to be given
the `-ffreestanding` flag explicitly for us to get a good binary;
- stop using ad-hoc tools/* scripts, and avoid the code-generation
anti-pattern overall on the build. Some of the generated files were
checked-in, and some were removed;
- remove empty files;
- use POSIX make(1) over gmake;
- add fuzz targets;
- partial "install" and "uninstall" targets;
- complete "clean" target.
The shortcomings are:
- only working on x86_64. More platforms coming soon;
- code is still messy: way too many warnings, GNU/BSD specific
extensions, inline assembly, and all kinds of unportable code;
- still only works with GCC and GCC-like compilers, and completly fails
with tcc(1) and cproc(1);
- the `deps.mk` file is being maintained manually. As I work on the
source files I'll finish automating its generation with `mkdeps.sh`;
- still seems to be coupled with Linux;
- still is missing tests setup;
- still uses `#include <$NAME.h>` instead of the correct
`#include "$NAME.h"` form.
The generated libgrovel.a did match the previous lib/libc.a 100%.
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gawk 5 complains.
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a register used as an index in the memory destination of a mov
instruction was wrongly interpreted as the destination of the mov.
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binary ops like ADD, AND, etc. modify the 2nd operand, not 1st.
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fdiv and fmul instructions were wrongly matched by the rules for
integer div and mul instructions, leading to incorrect conclusions
about register values being clobbered.
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There is a lot which could be common between i386 and x86_64, but none
of it will be useful for any other arch. These should be useful for
all archs, however.
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Some functions implemented in asm need to use EBP for purposes other
than acting as a frame pointer. (Notably, it is used for the 6th
argument to syscalls with 6 arguments.) Without frame pointers, GDB
can only show backtraces if it gets CFI information from a
.debug_frame or .eh_frame ELF section.
Rather than littering our asm with ugly .cfi directives, use an awk
script to insert them in the right places during the build process, so
GDB can keep track of where the current stack frame is relative to the
stack pointer. This means GDB can produce beautiful stack traces at
any given point when single-stepping through asm functions.
Additionally, when registers are saved on the stack and later
overwritten, emit ..cfi directives so GDB will know where they were
saved relative to the stack pointer. This way, when you look back up
the stack from within an asm function, you can still reliably print
the values of local variables in the caller.
If this awk script were to understand every possible wild and crazy
contortion that an asm programmer can do with the stack and registers,
and always emit the exact ..cfi directives needed for GDB to know what
the register values were in the preceding stack frame, it would
necessarily be as complex as a full x86 emulator. That way lies
madness.
Hence, we assume that the stack pointer will _only_ ever be adjusted
using push/pop or else add/sub with a constant. We do not attempt to
detect every possible way that a register value could be saved for
later use, just the simple and common ways.
Thanks to Szabolcs Nagy for suggesting numerous improvements to this
code.
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