bionic: linker_phdr: Introduce kPageSize
kPageSize is needed to determine whether the loader needs to
extend VMAs to avoid gaps in the memory map when loading the ELF.
While at it, use kPageSize to generically deduce the PMD size and
replace the hardcoded 2MB PMD size.
Bug: 316403210
Test: atest -c linker-unit-tests [Later patch]
Test: m && launch_cvd
Change-Id: Ie770320e629c38149dc75dae1deb1e429dd1acf2
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
diff --git a/linker/linker_phdr.cpp b/linker/linker_phdr.cpp
index 1ea79f0..85cd949 100644
--- a/linker/linker_phdr.cpp
+++ b/linker/linker_phdr.cpp
@@ -142,8 +142,18 @@
MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \
MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE))
-// Default PMD size for x86_64 and aarch64 (2MB).
-static constexpr size_t kPmdSize = (1UL << 21);
+static const size_t kPageSize = page_size();
+
+/*
+ * Generic PMD size calculation:
+ * - Each page table (PT) is of size 1 page.
+ * - Each page table entry (PTE) is of size 64 bits.
+ * - Each PTE locates one physical page frame (PFN) of size 1 page.
+ * - A PMD entry locates 1 page table (PT)
+ *
+ * PMD size = Num entries in a PT * page_size
+ */
+static const size_t kPmdSize = (kPageSize / sizeof(uint64_t)) * kPageSize;
ElfReader::ElfReader()
: did_read_(false), did_load_(false), fd_(-1), file_offset_(0), file_size_(0), phdr_num_(0),