PHP extension seg fault when modifying a zval by reference - php

Question

PHP:
$publickey = pack('H*', "03ca473d3c0cccbf600d1c89fa33b7f6b1f2b4c66f1f11986701f4b6cc4f54c360");
$pubkeylen = strlen($publickey);
$result = secp256k1_ec_pubkey_decompress($publickey, $pubkeylen);
C extension:
PHP_FUNCTION(secp256k1_ec_pubkey_decompress) {
secp256k1_start(SECP256K1_START_SIGN);
zval *pubkey, *pubkeylen;
unsigned char* newpubkey;
int newpubkeylen;
int result;
if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "zz", &pubkey, &pubkeylen) == FAILURE) {
return;
}
newpubkey = Z_STRVAL_P(pubkey);
newpubkeylen = Z_LVAL_P(pubkeylen);
result = secp256k1_ec_pubkey_decompress(newpubkey, &newpubkeylen);
if (result == 1) {
newpubkey[newpubkeylen] = 0U;
ZVAL_STRINGL(pubkey, newpubkey, newpubkeylen, 0);
ZVAL_LONG(pubkeylen, newpubkeylen);
}
RETURN_LONG(result);
}
the $publickey is decompressed from a 32 byte to a 65 byte string, for w/e reason when we're doing this we get a Segmentation Fault.
I asume we're doing something structurally wrong ... considering this is our first PHP extension.
full code; https://github.com/afk11/secp256k1-php

Answer 1

After looking at your extension code, you haven't linked the actual secp256k1 lib (.so) while building your extension ( #include "secp256k1.h" does not include actual bitcoin/secp256k1 code c library ).
You need to change your config.m4 in any of the following ways
1) Add "-l/path/to/bitcoin/secp256k1/lib" to the "gcc" options.
Help: here, I am talking about once you "make install" on
bitcoin/secp256k1, some libraries will be installed to /usr/lib or
/usr/lib64 or /usr/lib/secp256k1 etc....
-lsecp256k1
// i.e. something like...
PHP_NEW_EXTENSION(secp256k1, secp256k1.c, $ext_shared,, "-lsecp256k1 -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1")
2) Or, include actual *.c files in from actual secp256k1 library
PHP_NEW_EXTENSION(secp256k1, secp256k1.c ../secp256k1/src/secp256k1.c ../secp256k1/src/others.c, $ext_shared,, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1)
I would recommend option-1