From e801af6fba428bbac170018f9ff69e4596d06b3b Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Sun, 5 Feb 2017 02:39:12 +0000 Subject: Use PC-relative relocations for USDT probe sites on i386 and amd64. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When recording probe site addresses in the output DOF file, dtrace -G needs to emit relocations for the .SUNW_dof section in order to obtain the addresses of functions containing probe sites. DTrace expects the addresses to be relative to the base address of the final ELF file, and the amd64 USDT implementation was relying on some unspecified and incorrect behaviour in the base system GNU ld to achieve this. This change reimplements the probe site relocation handling to allow USDT to be used with lld and newer GNU binutils. Specifically, it makes use of R_X86_64_PC64/R_386_PC32 relocations to obtain the probe site address relative to the DOF file address, and adds and uses a new DOF relocation type which computes the final probe site address using these relative offsets. Reported by and discussed with: Rafael Espíndola MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D9374 --- cddl/contrib/opensolaris/lib/libdtrace/common/dt_dof.c | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) (limited to 'cddl/contrib/opensolaris/lib/libdtrace/common/dt_dof.c') diff --git a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_dof.c b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_dof.c index a4e325671f9f..3d1d976bd3dd 100644 --- a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_dof.c +++ b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_dof.c @@ -462,18 +462,8 @@ dof_add_probe(dt_idhash_t *dhp, dt_ident_t *idp, void *data) dt_buf_write(dtp, &ddo->ddo_enoffs, pip->pi_enoffs, pip->pi_nenoffs * sizeof (uint32_t), sizeof (uint32_t)); - /* - * If pi_rname isn't set, the relocation will be against the - * function name. If it is, the relocation will be against - * pi_rname. This will be used if the function is scoped - * locally so an alternate symbol is added for the purpose - * of this relocation. - */ - if (pip->pi_rname == NULL) - dofr.dofr_name = dofpr.dofpr_func; - else - dofr.dofr_name = dof_add_string(ddo, pip->pi_rname); - dofr.dofr_type = DOF_RELO_SETX; + dofr.dofr_name = dof_add_string(ddo, pip->pi_rname); + dofr.dofr_type = DOF_RELO_DOFREL; dofr.dofr_offset = dt_buf_len(&ddo->ddo_probes); dofr.dofr_data = 0; -- cgit v1.2.3