Preserve timestamps for installed headers to improve incremental builds #530
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kateinoigakukun
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This change makes it so that the timestamps of installed header files
are only updated when the contents of the header files change.
This change is beneficial for incremental builds of projects depending
on wasi-libc. For example, the Swift project builds wasi-libc as part
of its build process, and this change reduces the number of build
products in the Swift build that are unnecessarily rebuilt.
The following commands can be used to verify the changes:
```bash
make clean && make -j16 && (
cd sysroot && find . -name "*.h" -type f -exec stat -c '%n %y' {} \;
) > sysroot.v1.timestamp && \
make -j16 && (
cd sysroot && find . -name "*.h" -type f -exec stat -c '%n %y' {} \;
) > sysroot.v2.timestamp
diff sysroot.v1.timestamp sysroot.v2.timestamp
```
The diff should show no changes in timestamps.
kateinoigakukun
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This file was conditionally overwritten by Makefile, but it makes it difficult to generate the file by a regular make rule, so I changed to generate it in Makefile consistently.
| @@ -981,7 +988,7 @@ check-symbols: startup_files libc | |||
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| install: finish | |||
| mkdir -p "$(INSTALL_DIR)" | |||
| cp -r "$(SYSROOT)/lib" "$(SYSROOT)/share" "$(SYSROOT)/include" "$(INSTALL_DIR)" | |||
| cp -p -r "$(SYSROOT)/lib" "$(SYSROOT)/share" "$(SYSROOT)/include" "$(INSTALL_DIR)" | |||
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How about using cp -ar everywhere?
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-a has subtle behavior differences across implementations (e.g. darwin cp does not preserve hard link but GNU coreutils does.) and it's not a part of POSIX spec unlike -p https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/utilities/cp.html
So I prefer -p unless we have clear needs for -a
| $(SYSROOT_INC)/__wasi_snapshot.h: | ||
| mkdir -p "$(SYSROOT_INC)" | ||
| ifeq ($(WASI_SNAPSHOT), p2) | ||
| printf '#ifndef __wasilibc_use_wasip2\n#define __wasilibc_use_wasip2\n#endif\n' \ |
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I just kept the existing way but I don't find any reason not to use echo. Let me do that.
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Ah, we need to use printf for Windows... https://github.com/WebAssembly/wasi-libc/actions/runs/10618495813/job/29433860327?pr=530#step:9:99
kateinoigakukun
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This change makes it so that the timestamps of installed header files are only updated when the contents of the header files change. This change is beneficial for incremental builds of projects depending on wasi-libc. For example, the Swift project builds wasi-libc as part of its build process, and this change reduces the number of build products in the Swift build that are unnecessarily rebuilt.
The following commands can be used to verify the changes:
The diff should show no changes in timestamps.
Eventually, unnecessary copyings themselves should be skipped but it requires making the wasi-libc build system to support complete incremental build.