libdl: Do not access the ELF file while the allocator is locked.

- Load symbols before allocation.
- Parse reloc records and place any reloc recs in a cache to use
  while the allocator is locked.
- Relocate symbols after section allocation.
- Split section loading into allocation/locating and loading.
- Update all arch back-ends with a new reloc interface to control
  tramp handling.
- Add `-a` and `-t` to the object list shell command.

Closes #3741

1 files changed, 94 insertions, 0 deletions

diff --git a/cpukit/libdl/rtl-trampoline.h b/cpukit/libdl/rtl-trampoline.h
new file mode 100644
index 0000000000..e04c20863b
--- /dev/null
+++ b/cpukit/libdl/rtl-trampoline.h
@@ -0,0 +1,94 @@
+/*
+ *  COPYRIGHT (c) 2019 Chris Johns <chrisj@rtems.org>
+ *
+ *  The license and distribution terms for this file may be
+ *  found in the file LICENSE in this distribution or at
+ *  http://www.rtems.org/license/LICENSE.
+ */
+/**
+ * @file
+ *
+ * @ingroup rtems_rtl
+ *
+ * @brief RTEMS Run-Time Linker Object File Trampoline Relocations Table.
+ *
+ * Cache relocation records that could result in a trampoline. The unresolved
+ * symbol table holds variable the symbol name (length string) and the object
+ * file's relocation records that reference the unresolved symbol. The
+ * trampoline cache is an extension to this table to reuse the code and memory
+ * and support trampolines.
+ *
+ * Some architectures require trampolines or veneers to extend the range of
+ * some instructions. The compiler generates small optimized instructions
+ * assuming most destinations are within the range of the instruction. The
+ * instructions are smaller in size and can have a number of encodings with
+ * different ranges. If a relocation record points to a symbol that is out of
+ * range for the instruction a trampoline is used to extend the instruction's
+ * range. A trampoline is a small fragment of architecture specific
+ * instructions located within the range of the relocation record instruction
+ * that can reach the entire address range. The trampoline's execution is
+ * transparent to the execution of the object file.
+ *
+ * An object file that needs a trampoline has a table allocated close to the
+ * text section. It has to be close to ensure the largest possible object file
+ * can be spported. The number of slots in a table depends on:
+ *
+ *  # Location of the code
+ *  # The type of relocation records in the object file
+ *  # The instruction encoding the relocation record points too
+ *  # The landing address of the instruction
+ *
+ * The allocation of the text segment and the trampoline table have to happen
+ * with the allocator lock being locked and held to make sure no other
+ * allocations happen inbetween the text section allocation and the trampoline
+ * table. Holding an allocator lock limits what the link editor can do when
+ * when the default heap allocator is being used. If calls any operating
+ * system services including the file system use the same allocator a deadlock
+ * will occur. This creates a conflict between performing the allocations
+ * together and reading the instructions while holding the allocator lock.
+ *
+ * The trampoline cache holds the parsed relocation records that could result
+ * in a trampoline. These records can be exaimined after the allocation of the
+ * text segment to determine how many relocation record target's are out of
+ * range. The minimum range for a specific type of relocation record has to be
+ * used as the instructions cannot be loaded.
+ */
+
+#if !defined (_RTEMS_RTL_TRAMPOLINE_H_)
+#define _RTEMS_RTL_TRAMPOLINE_H_
+
+#include <rtems/rtl/rtl-unresolved.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/**
+ * Add a relocation to the list of trampolinr relocations.
+ *
+ * @param obj The object table the relocation record is for.
+ * @param flags Format specific flags.
+ * @param sect The target section number the relocation references.
+ * @param symvalue The symbol's value.
+ * @param rel The format specific relocation data.
+ * @retval true The relocation has been added.
+ * @retval false The relocation could not be added.
+ */
+bool rtems_rtl_trampoline_add (rtems_rtl_obj*        obj,
+                               const uint16_t        flags,
+                               const uint16_t        sect,
+                               const rtems_rtl_word  symvalue,
+                               const rtems_rtl_word* rel);
+
+/**
+ * Remove the relocation records for an object file.
+ *
+ * @param obj The object table the symbols are for.
+ */
+void rtems_rtl_trampoline_remove (rtems_rtl_obj* obj);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif