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Hi,<br>
<br>
The reason this happens is that Wasm functions can take a predefined
number of parameters only, they cannot be truly variadic. Variadic
functions are emulated by putting the extra arguments in memory and
passing a pointer ("memory index" in wasm) to the first one instead
of `...` part of the argument list. That's why printf takes two
arguments - first one is format string, the second is the pointer to
the rest of the arguments.<br>
<br>
Best,<br>
Petr
<p><br>
</p>
<div class="moz-cite-prefix">On 12/19/21 02:48, shankusu2017 via
llvm-dev wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CABC4HC9ra2hVkfKTNfGEimHQjUY6BtrAoNnyFN4sg85z32y-wA@mail.gmail.com">
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<div dir="ltr"><br>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">---------- Forwarded message
---------<br>
发件人： <strong class="gmail_sendername" dir="auto">shankusu2017</strong>
<span dir="auto"><<a href="mailto:shankusu2017@gmail.com"
moz-do-not-send="true" class="moz-txt-link-freetext">shankusu2017@gmail.com</a>></span><br>
Date: 2021年12月19日周日 18:17<br>
Subject: Fwd: about clang compile c to wasm lost argument<br>
To: <<a href="mailto:llvm-admin@lists.llvm.org"
moz-do-not-send="true" class="moz-txt-link-freetext">llvm-admin@lists.llvm.org</a>><br>
</div>
<br>
<br>
<div dir="ltr"><br>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">---------- Forwarded
message ---------<br>
发件人： <strong class="gmail_sendername" dir="auto">shankusu2017</strong>
<span dir="auto"><<a
href="mailto:shankusu2017@gmail.com" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">shankusu2017@gmail.com</a>></span><br>
Date: 2021年12月19日周日 18:15<br>
Subject: about clang compile c to wasm lost argument<br>
To: <<a href="mailto:surma@surma.dev" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">surma@surma.dev</a>><br>
</div>
<br>
<br>
<div dir="ltr">hi:
<div> I use clang to compile the c code into wasm, and
I found that clang13/14 regards the variable reference
in the c language as a parameter, such as the "..."
part in int printf(const char *format, ...); In this
way, when I implemented my own printf function in the
host environment, wasm only passed 2 parameters to the
host when calling prinf, but I actually passed more
than 2 parameters. This will cause the printf function
I implemented by myself to receive only 2 parameters,
and thus lose one parameter. The attachment contains
my original c code and compiled wasm and wat codes.
The green box part shows that the printf function only
accepts 2 input parameters. I don't know how to make
clang understand that the number of parameters
received by printf is uncertain. Is there any
solution?</div>
<div> follow build cmd:</div>
<div>clang -I ../../src/ --target=wasm32 -nostdlib
-Wl,--no-entry -Wl,--export-all -Wl,--allow-undefined
--sysroot=/usr printf.c -o ../.././build/printf.wasm<br>
</div>
<div>wabt</div>
<div><br>
</div>
<div>wasm2wat printf.wasm -o printf.wat<br>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
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