examples/linux64/hello-make: Example using single .c file and Makefile #39

pfalcon · 2020-01-05T09:12:36Z

And a linker script. Made possible by the inline assembly support, added
recently.

The sample still has to perform various workarounds of PPCI warts, which
rather be fixed before merging this sample.

codecov-io · 2020-01-05T09:16:11Z

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pfalcon · 2020-01-05T09:18:15Z

As the description says, I don't think this should be merged as is, rather, this should be an example and motivation to fix the issues spotted and submitted.

Currently, this is "blocked" on: #36 and #38 . The samples works around both issues, but that's the point: we should not give an example how to work around the issues, they should not be there in the first place.

windelbouwman · 2020-01-05T11:06:05Z

Nice job! I agree that the issues should be fixed before merging this example. Good example btw, and thanks for taking the time to test drive this project. Btw, you are probably one of the first test users, but I guess you already got that. Thanks for taking the time and reporting your experiences.

windelbouwman · 2020-01-05T11:07:17Z

examples/linux64/hello-make/hello.c

+// precluding from running as entrypoint).
+int _startup()
+{
+    asm("call main");


Note that I recently added multiline asm syntax support if you want to use it:

asm( "call main\n" "jmp exit\n" );

Note that I recently added multiline asm syntax

Well, I, multiline inline asm syntax wit those explicit \n's isn't particularly pretty, so given a choice, I used per-line asm's. But given that register info applies to the entire asm block, there's no choice, so will reformat as you suggest.

Oh, I mean, here there's no unavoidable need to reformat, but for consistency...

Well, I, multiline inline asm syntax wit those explicit \n's isn't particularly pretty

Fully agree, this is ugly, but it is an artifact of string literals being glued together at the lexer level in C, so that's probably why it is required.

windelbouwman · 2020-01-05T11:12:29Z

examples/linux64/hello-make/hello.c

+
+void syscall(int nr, int a, int b, int c)
+{
+    asm("mov rax, rdi"); // abi param 1


I added input parameters and clobber info to assembly code, so this should work as well:

asm( "mov rax, %0 \n" "mov rdi, %1 \n" "mov rsi, %2 \n" "mov rdx, %3 \n" "syscall \n" : : "r" (nr), "r" (a), "r" (b), "r" (c) // input registers, patched into %0 .. %3 : "rax", "rdi", "rsi", "rdx" // clobber registers, handled by the register allocator );

In this example, it might not make much sense, since we target linux anyways, but the code now makes some assumptions about the calling convention of the syscall function itself.

Off course, you might want to cross check the result of this with tools/ppci_explorer.py

In this example, it might not make much sense, since we target linux anyways, but the code now makes some assumptions about the calling convention of the syscall function itself.

Yeah, I guess where it comes into play is with optimizations and surrounding code. But it's definitely best practice to use it, and we want to show just that as example, so applying your suggested code verbatim.

windelbouwman · 2020-01-05T11:14:02Z

examples/linux64/hello-make/Makefile

+hello.all.o: hello.o
+	python -m ppci ld --layout linux64.ld $^ -o $@
+
+# We build object files as usual with $(CC) (using the builtin make rule).


Very cool that the builtin rule "just works" (tm)!

pfalcon · 2020-01-05T14:18:00Z

Good example btw, and thanks for taking the time to test drive this project. Btw, you are probably one of the first test users, but I guess you already got that.

Sure, I'm very well aware what happens when you give something you dearly worked on for some time into hands of other people - they start to bend and abuse it in unpredictable ways, and all hell breaks loose ;-). In my case, I also oftentimes work on minimalist projects, which are supposed to do only what they're supposed to do. That's why I go thru the trouble of discussing things I see missing in PPCI and would like to see added/changed.

Thanks for other comments - will act on them later.

pfalcon · 2020-01-09T16:19:11Z

Updated inline asm as was suggested in comments, and also removed explicit objcopy step, per #32 (comment). Now, this looks much cleaner and solid!

pfalcon · 2020-01-09T16:20:20Z

examples/linux64/hello-make/Makefile

@@ -0,0 +1,15 @@
+CC = python -m ppci cc
+CFLAGS = -O1


@windelbouwman: FYI, ppci-cc currently doesn't accept -O without arg, but it should (equivalent to -O1 per gcc).

Hmm, indeed, this is a impedance mismatch with gcc. The way I implemented now is with argparse and accepting a series of optimization levels. The other option is to make each optimization target a seperate command line argument.

The way I implemented now is with argparse and accepting a series of optimization levels.

Yeah, I see the problem. argparse allows to specify an argument to short option either without a space or not, i.e. ppci-cc -O1 and ppci-cc -O 1 are equivalent, and -O alone is not possible, as argparse expects an argument. gcc "solves" that by now allow a space:

$ gcc -c -O 1 hello.c gcc: error: 1: No such file or directory

The other option is to make each optimization target a seperate command line argument.

That would make things like -Os, -O1, etc. essentially long options, and I thought argparse hardcodes long options to have -- prefix. But trying:

+compile_parser.add_argument( + "-Ofoo", help="optimize code", action="store_true" +)

And running:

`ppci-cc -Ofoo`

doesn't lead to exceptions or visible artifacts. Oh, it's Python, so checking that it actually works is a matter of seconds:

Namespace(E=False, I=[], M=False, O='0', Ofoo=True, S=False, ast=False, c=True, define=[], freestanding=False, g=False, html_report=None, include=[], instrument_functions=False, ir=False, log=20, machine=None, mtune=[], output='hello.o', pycode=False, report=None, sources=[<_io.TextIOWrapper name='hello.c' mode='r' encoding='UTF-8'>], std='c99', super_verbose=False, text_report=None, trigraphs=False, undefine=[], verbose=0, wasm=False)

So, yep, seems to work, and hopefully it means we'll be able to achieve as close option compatibility with gcc as possible without switching to custom arg parser.

Okay, I suggest to fix this later, we'll figure a way :)

windelbouwman · 2020-01-09T20:57:28Z

examples/linux64/hello-make/hello.c

@@ -0,0 +1,58 @@
+// Currently, it's not possible to specify executable entrypoint to ppci
+// linker - so far, the entrypoint is at the beginning of the code segment.


I added the option to specify the entry point in the linker script by using:

ENTRY(startup)

Please refer to commit c078ba4 for the change.

Thanks for this improvement hint! I'm pretty happy with this change!

pfalcon · 2020-01-10T21:30:13Z

Ok, with resolution of #36, I updated this sample to be like I initially wanted it to be: when inline asm is only used to implement syscall(), and main() is the entrypoint. From my PoV, this is now ready to merge.

windelbouwman · 2020-01-11T10:18:32Z

examples/linux64/hello-make/linux64.ld

@@ -0,0 +1,9 @@
+MEMORY code LOCATION=0x40000 SIZE=0x10000 {
+    SECTION(reset)


This reset section can be removed. Note that you may want to add the ENTRY to main as well.

This reset section can be removed.

Ack. Was originally copied verbatim from the "hello" sample, but makes sense to remove any unneeded stuff to not confuse readers.

Yes, agreed, I'm removing it from the other sample code as well, to reduce clutter. The reset section was needed before the entry point option.

Note that you may want to add the ENTRY to main as well.

I pass it on the command line instead. The whole idea of this example is to show how to do things from command-line interface.

For as long as this "memory map layout" files aren't compatible with GNU ld "linker scripts", I'd personally prefer to avoid using them too much ;-). (I know that "ENTRY(sym)" syntax is exactly compatiable with GNU ld, thanks for that.)

Ah, okay, I missed that, thanks!

windelbouwman · 2020-01-11T10:19:42Z

examples/linux64/hello-make/Makefile

+# Now link all compiled objects (here, just one) into executable. For this,
+# we need to provide linker with memory layout file. We'll also use main()
+# as the executable entrypoint.
+hello: hello.o


I tried to put the linux64.ld file as dependency as well (since it is a dependency), but that did not work due to the nature of the $^ variable.

I tried to put the linux64.ld file as dependency as well (since it is a dependency), but that did not work due to the nature of the $^ variable.

Yep. You either need to get rid of special vars, using "materialized" file list, or so-called order-only dependencies might help, but few people know about them, so using them might be confusing. This is again to show simple, clear, concise usage.

And a linker script. Made possible by the inline assembly support, added recently. The sample still has to perform various workarounds of PPCI warts, which rather be fixed before merging this sample.

pfalcon · 2020-01-11T11:10:26Z

Pushed update with:

-    SECTION(reset)
-    ALIGN(4)

(yanked that ALIGN too, as it's already aligned, let's show people the simplest possible usage).

windelbouwman reviewed Jan 5, 2020

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pfalcon force-pushed the example-hello-make branch from a152193 to ca742e5 Compare January 9, 2020 16:18

pfalcon commented Jan 9, 2020

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windelbouwman reviewed Jan 9, 2020

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pfalcon force-pushed the example-hello-make branch from ca742e5 to 017ee66 Compare January 10, 2020 21:27

pfalcon changed the title ~~WIP: examples/linux64/hello-make: Example using single .c file and Makefile~~ examples/linux64/hello-make: Example using single .c file and Makefile Jan 10, 2020

windelbouwman reviewed Jan 11, 2020

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examples/linux64/hello-make: Example using single .c file and Makefile

629ff58

And a linker script. Made possible by the inline assembly support, added recently. The sample still has to perform various workarounds of PPCI warts, which rather be fixed before merging this sample.

pfalcon force-pushed the example-hello-make branch from 017ee66 to 629ff58 Compare January 11, 2020 11:09

windelbouwman merged commit 942e880 into windelbouwman:master Jan 11, 2020

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examples/linux64/hello-make: Example using single .c file and Makefile #39

examples/linux64/hello-make: Example using single .c file and Makefile #39

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pfalcon commented Jan 11, 2020

		@@ -0,0 +1,58 @@
		// Currently, it's not possible to specify executable entrypoint to ppci
		// linker - so far, the entrypoint is at the beginning of the code segment.

		@@ -0,0 +1,9 @@
		MEMORY code LOCATION=0x40000 SIZE=0x10000 {
		SECTION(reset)

examples/linux64/hello-make: Example using single .c file and Makefile #39

examples/linux64/hello-make: Example using single .c file and Makefile #39

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pfalcon commented Jan 11, 2020

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