Add proper tracing options, remove getenv calls from enclave code.

[wintersteiger]

This adds proper tracing options, which removes the need for getenv calls in the enclave. Fixes #780.

Goes with lsds/sgx-lkl-musl#36.

[wintersteiger]

There's one relevant getenv call in musl, see https://github.com/lsds/sgx-lkl-musl/blob/a6360f883fd906b18c1878254547ad72da28d7e6/ldso/dynlink.c#L822. This is now the only tracing/debug env var that gets passed through to the enclave as an env var:

sgx-lkl/src/main-oe/sgxlkl_params.c

Line 3 in 9979a88

const char* sgxlkl_auto_passthrough[1] = {"SGXLKL_DEBUGMOUNT"};

I'm not sure this is still useful (see bunch of commented code further up in the file). Can I remove it?

[prp]

LGTM, left minor questions.

[prp]

There's one relevant getenv call in musl, see https://github.com/lsds/sgx-lkl-musl/blob/a6360f883fd906b18c1878254547ad72da28d7e6/ldso/dynlink.c#L822. This is now the only tracing/debug env var that gets passed through to the enclave as an env var:

sgx-lkl/src/main-oe/sgxlkl_params.c

Line 3 in 9979a88

const char* sgxlkl_auto_passthrough[1] = {"SGXLKL_DEBUGMOUNT"};

I'm not sure this is still useful (see bunch of commented code further up in the file). Can I remove it?

This is part of a mechanism that, instead of loading debug symbols inside the enclave and then passing a pointer to gdb, it allows the enclave image to be mounted outside and thus gdb can access the files with symbols directly. For large applications (e.g. TF), this results in much better performance during debugging.

[wintersteiger]

Great, thanks for the explanation, then it makes sense to keep it!